Durable foam of olefin polymers, methods of making foam and articles prepared from same

ABSTRACT

Olefin polymer-based, durable, open-cell foam compositions, structures and articles derived from same; methods for preparation of such foams; and use of the dry durable foams in various applications are disclosed. Further described is use of the foams and structures and articles made of same in absorption, filtration, insulation, cushioning and backing applications, and in particular for odor removal, hygiene and medical applications due to, among other properties, good absorption capabilities, softness and/or flexibility of the foams and their recyclable nature.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of the U.S.application Ser. No. 11/069,843, filed Feb. 28, 2005 now U.S. Pat. No.7,361,694, which claims priority from the U.S. Provisional ApplicationNo. 60/548,493, filed Feb. 27, 2004; each application is incorporatedherein, in its entirety, by reference.

BACKGROUND

Hydrophilic, open-cell foams find utility in products for acquiring anddistributing aqueous fluids; for example: diapers, adult incontinencepads and briefs, feminine hygiene products, wiping towels and sponges,wound dressings and surgical sponges, and other analogous aqueousfluid-absorption uses. Additionally, both hydrophobic and hydrophilic,open-cell foams may find use in numerous other applications, for examplefluid filtration, insulation applications, e.g., sound absorption orsound deadening and heat or cold insulation or barriers, cushioning,carpet and fabric backing.

The invention pertains to recyclable, durable, open-cell foamcompositions, structures and articles derived from same; and methods forpreparation and use of such foams. It further pertains to use of the drydurable foams in the absorption, filtration, insulation, cushioning andbacking applications by virtue of, among other properties, their goodabsorption capabilities, softness and/or flexibility and theirrecyclable nature.

Mechanically frothed-derived foam, useful in articles for acquiring anddistributing aqueous fluids have been prepared from polymeric latex; forexample, carboxylated styrene-butadiene latex-derived foams described inU.S. Pat. Nos. 4,990,541; 5,387,207 and WO-01/80916A2.

Aqueous dispersions of linear olefin copolymers, useful for preparingdoctored film coatings are made, but apparently not frothed, using astabilizing and emulsifying amount of surfactant as described in U.S.Pat. No. 5,798,410.

SUMMARY OF THE INVENTION

The invention comprises open-cell, durable, olefin polymer foamcompositions; methods for preparation of such durable foams; and the useof the durable foams in various applications. The relative softness andflexibility of the foams and their good aqueous fluid absorption andaqueous fluid-wicking capability makes them of particular usefulness inabsorbent hygiene articles having, among other properties, fluidabsorption and wicking capabilities.

We have discovered an open-cell foam that is prepared from aqueous-baseddispersed olefin polymer froth and exhibits high Absorbency Capacity(“AC”) (expressed as g of synthetic 0.9 wt. percent saline solutionabsorbed per g dry foam) of greater than 10 g/g, preferably greater than15 g/g. The durable foam of the invention preferably is hydrophilic andfor selected applications is capable of vertically wicking the described0.9% saline solution to a height preferably of greater than about 5 cm(˜2 in), more preferably greater than about 8 cm (˜3 in), even morepreferably greater than about 10 cm (˜4 in), and most preferably togreater than about 15 cm (˜6 in). Vertical wicking ability is measuredby a test of Vertical Wicking Height (“VWH”), described in greaterdetail below.

The aqueous-based, dispersed olefin polymer froth suitably used to makefoam of the invention is prepared from a semi-crystalline,thermoformable polymer (Polymer). This provides an added advantage ofimparting a recyclable character to the resulting durable foam itselfand to articles that incorporate it. In the case of sound and thermalinsulation and cushioning applications, in particular, this makes it avery attractive material from which to fabricate articles, e.g.,automobile seat cushioning, headliners and sound insulation components,carpet backing for autos or homes, furniture cushioning and mattressesand padding, gas or liquid filtration devices and in related and similarapplications. In such uses it is highly desirable to have an olefinpolymer-based, open-cell foam element that can be easily recycled.

The Polymer is selected from copolymers and interpolymers of ethyleneand/or propylene and other monomers selected from C₄ to C₁₀ olefins,preferably alpha-olefins, and more preferably selected from n-butene,n-hexene and n-octene. The ethylene or propylene content of Polymerranges from about 2-98 percent of Polymer. The modulus of the durablefoam can be controlled by selection of polymers. For example, using acopolymer having a higher level of C₄-C₈ olefins will give a softer andmore flexible foam than a copolymer having lower amounts of C₄-C₈olefins. Similarly, a foam made with propylene/C₄-C₈ olefin copolymerwill give a stiffer foam than a corresponding composition made withethylene/C₄-C₈ olefin copolymer. Selected comonomer(s) make up theremainder of the Polymer. Further details regarding the Polymer arefound below.

The absorbent, open-cell Foam composition of the invention is a durableFoam. It results from drying of an aqueous, frothed dispersion ofPolymer under conditions selected to inhibit the coalescence of theindividual gas bubbles in the Froth for a time period sufficient toallow dispersed Polymer particles contained in the thin aqueous layersurrounding the entrapped air bubble to fuse before the aqueous filmstructure undergoes significant collapse. Drying occurs as the waterevaporates from the bubbles' surfaces and from the channels orinterstices between the bubbles.

Some preferred modes of use and articles comprised of the absorbent Foaminclude aqueous-fluid absorbent, conformable hygiene articles, moreparticularly baby diapers, adult incontinence products, feminine hygieneproducts, nursing pads, sweat bands, wiping toweling and sponges, wounddressing pads, surgical sponges, medical garments, surgical drapery andfood packaging absorbent padding. Such padding typically is employed forabsorbing meat juice and drippings at the bottom of food packagingtrays. The foam is also useful in articles used for timed-releasedelivery systems, for example as in sustained delivery of pharmaceuticaland drug products, as through skin contact patches and the like.

The invention further comprises recyclable, absorbent articles. In thecase of generally non-disposable articles of a more permanent andreusable character, such as sound and thermal insulation and cushioningapplications, in particular, the recyclable nature makes the absorbentFoam a very attractive material from which to fabricate articles. Thisis due to their impact-absorption, sound absorption or otherabsorption-related properties; for example, in automobile seatcushioning, headliners and sound insulation components, carpet backingfor autos or homes, furniture cushioning and mattresses and padding, gasor liquid filtering devices and similar applications.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 represents a melting curve, heat flow in watts/gram (W/g) plottedagainst temperature (in deg Celsius) on the x-axis, obtained by firstheat differential scanning calorimetry (DSC) for the ethylene copolymerdesignated as Polymer 1D in Table-1 and elsewhere. The endotherm plot ofa DSC curve may be used to determine an approximate melting temperaturerange for the respective Polymer, as well as to determine thetemperature (T_(x % c)) for a given percentage of Polymer residualcrystallinity, as described more fully and utilized for purposes notedbelow.

DETAILED DESCRIPTION OF THE INVENTION

All percentages and parts, unless otherwise stated, are expressed byweight.

Definition of Terms

The term Conformable as used here means the ability to bend and flex tothe shape desired by the user; for example, the shape of a wearer of anabsorbent article. The term Dispersion as used here means a two phaseliquid/polymer composition where the aqueous phase is normally thecontinuous phase and the Polymer is suspended therein in a stablefashion, suitably with the aid of a dispersing agent/dispersant so thatthe polymer will remain dispersed at least for as long as it willrequire to complete the frothing step. Preferably the polymer willremain dispersed throughout the entire frothing and drying process sothat a complete process can be conducted, either batch-wise or in acontinuous fashion, without the polymers settling out of the dispersion.Suitable methods are taught in the art; see for example U.S. Pat. Nos.5,798,410 and 6,448,321.

The term Drying as used here means a process of causing a Froth tobecome a Dry Foam and the term Dry as used herein means elimination ofat least 95 percent of the water from the Froth.

The term Frothing or Frothed as used here means a process ofincorporating substantial volumes of air, or other gas, in a liquidwhere at least 80, preferably at least 85 and more preferably at least90 volume percent of the frothed material consists of the gaseouscomponent. It is understood that the aqueous liquid can be a molecularsolution, a micellar solution or a dispersion. In general the froth iscreated by mechanical methods such as high shear mixing underatmospheric conditions or optionally injecting gas into the system whilemixing.

The term Froth as used here means an aqueous dispersion of the Polymerwhich has been Frothed, as described above, before Drying.

The term Foam as used here means a durable structure having an open cellcontent of at least 80% or greater, preferably at least 85% or greaterand more preferably at least 90 percent or greater, as determined by andaccording to ASTM D2856-A.

The term Major Surface as used here means, in a Foam, one of twosubstantially parallel surfaces of largest area, in contrast to a minorsurface thereof. While possible to cut and trim a raw foam in a mannerto form a six surface, regular three dimensional cubical geometricalstructure, where all six Foam surfaces are of substantially the samearea, because of the practical nature of continuously generating a foamarticle, it's normally accomplished by spreading frothed material on aconveyer moving in the x-direction, of y-dimension Froth width, andz-dimension Froth thickness. The z-axis or z-direction means the axissubstantially perpendicular (orthogonal) to the xy-plane defined by thesurface of such a conveyor and therefore generally perpendicular to aMajor Surface of the Foam as generated. Two major Froth surfaces ofx-length and y-width, which when dried to Foam results in a threedimensional Foam structure of surface area equal to about xy on both thetop and bottom. It is each of these top and bottom Foam surfaces thatare referred to here as a Major Surface, or in the case of Foam that hasbeen slit into pieces of approximately equal thickness along the x-yaxes, Major Surface means the resulting larger parallel surface on eachopposite, parallel side of each of the resulting slit sheets of Foam.

Olefin Polymers

The semi-crystalline olefin polymer (Polymer) is selected fromcopolymers and interpolymers of ethylene and/or propylene and othermonomers selected from C₄ to C₁₀ olefins, preferably alpha-olefins, morepreferably from C₄ to C₈ alpha-olefins and most preferably selected fromn-butene, n-hexene and n-octene. The ethylene or propylene content ofthe Polymer ranges from about 2-98 wt. percent of Polymer.

Where a softer, more flexible foam is desired a primarily ethylene-basedpolyolefin is selected in which ethylene comprises from about 98 to 65percent of Polymer. Where a stiffer foam of greater flexural modulus isdesired, a primarily propylene-based polyolefin may be selected,propylene comprising from about 98 to 65 percent of the Polymer.Selected comonomer(s) make up the remainder of the Polymer.

The Polymer has the following characteristics and properties:

-   -   1) Crystallinity as determined by the observance of at least one        endotherm when subjected to standard differential scanning        calorimetry (DSC) evaluation (see for illustration purposes,        FIG. 1);    -   2) for ethylene-based Polymers a melt index (“MI”) determined        according to ASTM D1238 at 190 deg C. (375 deg F.) with a 2.16        kg (4.75 lb) weight (i.e., condition 190 C./2.16 kg) of about 30        or less, preferably of about 25 or less, more preferably of        about 22 or less, and most preferably of about 18 g/10 min or        less and about 0.1 or greater, preferably about 0.25 or greater,        more preferably about 0.5 or greater, and most preferably about        0.75 g/10 min or greater; and for 1-propene-based Polymers a        Melt Flow Rate (“MFR”) determined according to ASTM D1238 at 230        deg C. (446 deg F.) with a 2.16 kg (4.75 lb) weight (i.e.,        condition 230 C./2.16 kg) of about 85 or less, preferably of        about 70 or less, more preferably of about 60 or less, and most        preferably of about 50 g/10 min or less and about 0.25 or        greater, preferably about 0.7 or greater, more preferably about        1.4 or greater, and most preferably about 2 g/10 min or greater.    -   3) for ethylene-based Polymers a density of about 0.845 or        greater, preferably about 0.85 or greater, more preferably about        0.855 and most preferably about 0.86 g/cc or greater, and about        0.925 or less and preferably about 0.91 g/cc or less, more        preferably about 0.905 or less, and most preferably about 0.90        g/cc or less; and for 1-propene-based Polymers because density        is a less commonly used measure of the backbone composition than        for ethylene Polymers, a 1-propene based Polymer comprises about        5 percent or greater, preferably about 7 percent or greater and        about 35 percent or less, preferably about 25 percent or less        comonomer content.

One class of Polymers particularly suited to use in the invention arecopolymers of ethylene and 1-octene or 1-butene, where ethylenecomprises from about 90 or less, preferably about 85 or less to about 50or greater, preferably about 55 or greater, and 1-octene or 1-butenefrom about 10 or greater, preferably about 15 or greater to about 50 orless, preferably to about 45 or less percent by weight of the copolymer,and that have Melt Index of about 0.25 or greater, preferably about 0.5or greater and about 30 or less, preferably about 20 or less g/10 min.

Another particularly preferred class of Polymers for use in theinvention are copolymers of 1-propene and ethylene, 1-octene, 1-hexeneor 1-butene, where 1-propene comprises from about 95 or less, preferablyabout 93 or less to about 65 or greater, preferably about 75 or greater,and ethylene, 1-octene, 1-hexene or 1-butene comprise from about 5 orgreater, more preferably about 7 or greater to about 35 or less,preferably 25 or less percent by weight of the copolymer, and that havea Melt Flow Rate of about 0.7 or greater, preferably about 1.4 g/10 minor greater and about 85 or less, and preferably about 55 g/10 min orless.

Alternatively, instead of a single Polymer a blend of polymers may beemployed that has the physical characteristics described above. Forexample, it may be desirable to blend a first polymer with relativelyhigh MI or MFR that is outside the range described above, with anotherof relatively low MI or MFR, so that the combined MI or MFR and theaveraged density of the blend fall within the ranges noted above. A morecrystalline alpha-olefin polymer may be combined with one of relativelylower crystallinity, such as one having a significant amount of longchain branching, to provide a blend that has substantially equivalentprocessing capability in preparing a stable Froth and the resultantdurable Foam of the invention. Where reference is made to a “Polymer” inthis specification, it is understood that blends of olefin polymers withequivalent physical characteristics may be employed with like effect andare considered to fall within our description of the invention.

A particularly preferred class of Polymer when used without otherpolymers or film forming additives, is characterized by exhibiting aparticular type of DSC plot of the Polymer's endotherm. In the preferredclass, the observed endotherm exhibits a relatively gentle slope as thescanning temperature is increased past the final endotherm maximum(i.e., the last inflection point on the DSC curve, e.g., point A foundon FIG. 1, where the curve slope becomes positive and the curve thenreturns to baseline state). This reflects a polymer of broad meltingrange rather than a polymer having what is generally considered to be asharp melting point.

Consequently, the drying temperature of Froth prepared from such apreferred Polymer can be more easily maintained at or near a point(e.g., point B on FIG. 1.) on the endotherm curve a significant distancefrom the return to baseline temperature at which point a major part, butnot all, of the crystalline portions the Polymer are melted and allowthe remaining Polymer particles to fuse or coalesce via their amorphousregions. In that fashion, by maintaining such a temperature during theFroth drying process most of the Polymer is allowed to fuse without acomplete loss of Polymer crystallinity and resultant tensile strength,and the bubble collapse that would otherwise ensue, if all crystallineportions of the Polymer were to be melted quickly. One method todetermine the maximum temperature at which to conduct Froth drying thatis below the point where such a loss of tensile strength would occur, isto calculate a temperature (T_(x % c)) where approximately x % residualcrystallinity remains in the selected Polymer. For a given Polymer, thefactor used to convert specific heat of melting into nominal weightpercent crystallinity in that Polymer can be determined from the meltingendotherm (as represented by a DSC curve) for that Polymer. For theethylene-based polymer designated as Polymer 1D in Table-1, a typicalfirst melt endotherm plot is represented by FIG. 1. To prepare a samplefor DSC analysis, a Polymer or Polymer foam sample may be compressionmolded by first heating sample to a temperature great enough toeliminate all crystallinity (about 190 deg C. for ethylene-based Polymerand about 230 deg C. for propylene-based Polymer), and then cooling inthe compression mold at a rate of 10 deg C./min. Prior to the DSCanalysis the compression molded sample is then aged for at least twodays, and preferably at least a week, at room temperature. The DSCendotherm is, likewise, generated using a heating rate of 10 deg C./min.The factor used to convert specific heat of melting into nominal weightpercent crystallinity for an ethylene-based polymer is 292 joules/gram(J/g)=100 wt % crystallinity. From the endotherm plot, a specific heatof melting ΔH_(m) of the Polymer in J/g can be determined by integratingthe area between the endotherm plot and the baseline. With the notedfactor, the total crystallinity of a sample (units: wt % crystallinity)is calculated as 100% times ΔH_(m) divided by 292 J/g. Using thisconversion factor, 1% residual crystallinity corresponds to 2.92 J/g, 2%corresponds to 5.84 J/g, and so forth, for ethylene-based polymers.

Accordingly, using this relationship, for the Polymer represented in theDSC of FIG. 1, T_(x % c) is defined by the temperature at which heat ofmelting on the higher temperature side of the perpendicular dropped tothe baseline at that temperature corresponds to x % crystallinity. Suchcalculations (often referred to as partial area calculations)_are easilydone using standard software supplied with a DSC instrument. Hence,T_(1% c) refers to the temperature, determined from the first heat DSCendotherm by partial area calculation using perpendicular drop to thebase line, at which 1% crystallinity (e.g., 2.92 J/g for ethylene-basedcopolymer) is obtained. For a propylene-based polymer, a factor of 165J/g is substituted in similar fashion and used to calculate the residualcrystallinity of the polymer at a specific temperature on the endothermrepresented by its respective DSC first heat plot. To provide adequateresidual crystallinity and tensile strength and avoid Froth bubblecollapse when drying, one would suitably operate at T_(x % c) on the DSCplot that represents greater than about 1, preferably greater than about1.5 and more preferably greater than about 2 weight and suitably lessthan about 5, preferably less than about 4 and more preferably less thanabout 3 weight percent, residual Polymer crystallinity, or roughlysomewhere in the region between about point A and point B on the plot ofFIG. 1. If a blend is to be used, for example a blend of propylene-basedpolymer with an ethylene-based polymer, the polymers will normally beimmiscible or partially miscible and one polymer becomes the continuousphase and the other the non-continuous phase. To determine anappropriate drying temperature range, it is the properties of thecontinuous polymer phase that one then measures, using the same DSCpartial area calculation as described above, to determine a desiredT_(x % c).

Dispersing Agents (Dispersants)

The Dispersant is employed in an amount of more than about 1%,preferably more than about 2%, and more preferably more than about 3%;up to an amount less than about 10%, preferably less than about 8%, andmore preferably less than 5%, based upon the weight of the aqueousdispersion of the Polymer.

The Dispersant used to create the relatively stable, aqueous dispersionof Polymer particles to be suitably used in practice of the inventionwill vary by the nature of the Polymer employed. The same or a differentDispersant may be used to serve as the frothing surfactant in thesubsequent preparation of the Froth.

Suitable Dispersants for the Polymer are salts of fatty acid(s) ofcarbon chain length of greater than 12 and preferably from 18 to 36carbon atoms. The salts are suitably alkali metal or ammonium salts ofthe fatty acid, prepared by neutralization of the acid with thecorresponding base, e.g., NaOH, KOH, and NH₄OH. These salts may beformed in situ in the dispersion step, as described more fully below.The appropriate fatty acid Dispersant is selected to serve as Dispersantfor the extrusion melt step in order to attain the desired averageparticle size of the Polymer, suitably between about 0.2-25 microns andpreferably between about 0.5-10 microns. Routine experimentation candetermine the type and quantity of Dispersant that provides a dispersionof the desired average particle size.

Frothing Surfactants

Creating and stabilizing the Froth during the frothing and drying stepis suitably accomplished by addition of a frothing surfactant to theaqueous dispersion of the Polymer when initially creating the Froth. Inaddition these surfactants can be used to improve aqueous wetting, ifdesired. Suitable frothing surfactants are selected primarily from butare not limited to, cationic, nonionic and anionic surfactants. Anionicsurfactants are preferred.

Cationic surfactants such as primary amine salts, diamine salts,quaternary ammonium salts and ethoxylated amines and the like may beused, as may nonionic surfactants such as alkylphenol ethoxylates,linear and secondary alcohol ethoxylates of alkyl group containing morethan 8 carbon atoms.

Anionic surfactants to be used in preparation of the Froth from apreviously created Dispersion of the Polymer are suitably selected fromcarboxylic acid salts and ester amides of carboxylic fatty acids,preferably fatty acids comprising from 12-36 carbon atoms, e.g., stearicor lauric acid, palmitic, myristic, oleic, linoleic, ricinoleic, erucicacid and the like. More preferred are those fatty acids comprising from12-24 carbon atoms, particularly their alkali metal (most preferablysodium or potassium), alkanolamine or ammonium salts. When a good “hand”or fabric like feel is desired in the finished Foam, a saturated fattyacid derivative (e.g., the salt of stearic or palmitic acid) ispreferably employed. Other suitable anionic surfactants includealkylbenzene sulfonates, secondary n-alkane sulfonates, alpha-olefinsulfonates, dialkyl diphenylene oxide sulfonates, sulfosuccinate esters,isethionates, linear alkyl (alcohol) sulfates and linear alcohol ethersulfates. It is understood that these frothing surfactants may or maynot be different than those used to prepare the dispersion. Thesesurfactants serve both to assist in Froth formation and help tostabilize the Froth. The most preferred frothing surfactants, whenrequired, are the alkali metal (more preferably sodium or potassium),mono-, di- and tri-alkanol (more preferably mono-, di- or triethanol)amine and ammonium salts of lauryl sulfate, dodecylbenzene sulfates,alcohol ethoxy sulfates, isethionates, and the dibasic salt ofN-octyldecylsulfosuccinimate, as well as mixtures of same.

Dispersion Step

The selected Polymer is dispersed in water, suitably by adding thePolymer and the selected Dispersant(s) in the desired amounts, and in ametered fashion, to the hopper of a bi-axial, polymer extruder wherethey are melt-kneaded at a temperature of about 220 deg C. (about 430deg. F.). Preferably, when using an ethylene-based olefin Polymer, along chain fatty acid of greater than 18 carbon atoms is melt-kneadedwith the Polymer. Then deionized water and base (e.g., KOH) sufficientto form in situ the fatty acid salt of Dispersant, are added at about165 deg. C. (˜330 deg F.) to the melt under a pressure of at least 410psi (˜2,800 kPa) to produce the Dispersion. Pressure within the extruderbarrel is maintained above the saturated steam pressure of roughly 20 to35 atmospheres (˜2,000 to ˜3,500 kPa) to avoid “blowback” through spacebetween the barrel and screw of the extruder, by ensuring that space isessentially full of the Dispersion. Then the Dispersion is diluted withdeionized water at a separate port downstream in the extruder barrel atabout 193 deg C. (˜380 deg F.) and at about 14 atmospheres (˜1,400 kPa)to produce a final Dispersion of about 67 percent solids. Dispersion isconducted from the extruder and collected, after passing through a mildcooling zone to prevent flashing of the water from the Dispersion, at atemperature of about 94 deg C. (˜200 deg F.).

Froth Preparation

A froth is prepared from the Dispersion of the Polymer by using a highshear, mechanical mixing process to entrain air or another gas in theaqueous phase of the Dispersion. The amount of air or other gas (where agas in addition to or other than air is desirable) to be incorporated inthe Froth suitably comprises at least 80, preferably at least 85, andmore preferably at least 90 percent by volume of the resultant Froth. Ingeneral, all components to be used in making the froth are mixedtogether with mild agitation to avoid entrapping air. Once all of theingredients are well mixed, the composition is exposed to high shearmechanical mixing. During this step the bulk viscosity increases as moreair is entrapped within the continuous aqueous phase. The mixture ismixed until a non-flowable, stiff froth is formed. This generallyproduces a froth with density of less than about 100 g/L. The time toreach this stage varies with amount and type of frothing surfactant andthe amount of mechanical shear. Any mechanical mixing device capable ofwhipping air into a thickened aqueous dispersion, such as a kitchenblender/hand mixer, Hobart mixer fitted with a wire whip or on a largerscale a Cowie-Riding Twin Foamer (Cowie Riding Ltd., G.B Patent1,390,180). The commercial foamers also allow one to inject air intotheir high shear mixing head to obtain very low (less than 50 g/L)density Froth.

Additives

The Foam of the invention may contain filler materials in amounts,depending on the application for which they are designed, ranging fromabout 2-100 percent (dry basis) of the weight of the Polymer component.These optional ingredients may include, but are not limited to, calciumcarbonate, titanium dioxide powder, polymer particles, hollow glassspheres, polymeric fibers such as polyolefin based staple monofilamentsand the like. Foam designed for use in the absorbent articles maycontain bulk liquid-absorbing material, such as short cotton fiber orother cellulose fiber evenly distributed throughout the polymer foam.Although they are not typically blended with the Polymer dispersionbefore frothing, due to their strong water absorbent nature, fineparticles of super absorbent polymer (“SAP”) a lightly cross-linkedacrylate polymer, can be evenly distributed upon the surface of theFroth just as it is entering the drying process to provide a durableFoam with extra absorbent properties on that surface when dried.However, if SAP particles are treated (e.g., with a surface layer ofdelayed water-solubility polymer such as, for example, a hydroxypropylalkylcellulose ether or a polyoxyethylene resin), to reduce theparticles' initial rate of water absorbency until after the Froth hasreached the dry Foam state, such “retarded-absorbency” SAP particles maybeneficially be added directly to the Polymer dispersion before frothingis initiated.

Other Foam end-uses such as cushioning, particularly flooring backing,can benefit from the addition of low cost fillers such as calciumcarbonate or titanium dioxide powder, and similar inert fillers such aspolymeric staple fibers. Such additives and fillers can enhance thephysical strength and/or the appearance of the resultant composite Foamafter drying, as well as to retain or to increase the Foam's impact orother absorption capabilities. For example, about 1-25% such cellulosefiber material of fiber length of about 0.25-35 mm (about 0.01-1.6 in)and preferably of about 0.5-30 mm (about 0.02-1.2 in), may be addedwithout substantial detriment to the absorption performance orstructural integrity of the Foam and in fact do enhance durability andstructural integrity of the Foam. For some Foam applications, it may bedesirable to incorporate one or more antioxidants and/or otherstabilizing agents to enhance the resistance of the Foam to oxidizationand yellowing from exposure to harsh conditions and weathering.

Synthetic latex polymers (e.g., styrenic or acrylic lattices) and/orother film-forming polymers may also be utilized as additives to theFroth to form stable and durable Foams and may aid in processing of theFroth and conversion to Foam by contributing to enhanced coalescence ofthe Polymer particles at both lower and higher drying temperatures. Ifutilized, such lattices or other film-forming polymers are suitablyemployed at levels of about 10-40 percent, dry weight basis, of thePolymer. When additives are to be incorporated in the Foam, they aresuitably added in the specified amounts to the dispersion of the Polymerbefore the Froth is prepared in the frothing step. However, aspreviously noted above, when water soluble or highly hygroscopicadditives (such as SAP) are desirable to add, they are added to theFroth surface immediately before the drying step or are injected intothe finished durable Foam.

Another additive that is preferably included in the Foam is an odoradsorptive agent, such as activated charcoal, to impart odor absorbingproperties to the Foam. The Foam can then be utilized in variousapplications where such properties are useful, for example in personalhygiene absorbent articles, shoe sole inserts, air filters and the like.The adsorptive agent is suitably utilized in a particulate form that isphysically incorporated into the Froth and ultimately in the finishedFoam. The Foam can be appropriately molded or cut to obtain articles ofvarious shapes to fit the use intended. By way of example, whenactivated charcoal is employed, the particles are distributed uniformlythroughout the Froth, suitably by mechanical mixing into the Dispersionand retain such distribution in the finished Foam. The average size ofadsorptive particles will be selected both for the maximum adsorptioneffect as well as their ability to remain uniformly distributed in theFroth before fully dried to form the Foam. Suitable average particlesize for activated charcoal is from about 1 micrometer to about 600micrometers, preferably greater than 10 micrometers, more preferablygreater than 100 micrometers and preferably smaller than 400micrometers, more preferably smaller than 200 micrometers. The amount ofactivated charcoal to be dispersed will be selected according to the enduse, but typically is from about 2 to about 18 wt. percent based on drypolymer solids in the Dispersion; preferably the amount used will begreater than 4, more preferably greater than 8 percent and preferablyless than 12, more preferably less than 10 percent. Optimum amounts ofother adsorptive materials can be determined by simple trial and errorexperimentation, but excessive amounts may cause excessive Froth densityor bubble collapse and are to be avoided.

Froth Stabilization Agents

Water-soluble, film-forming natural and synthetic polymers such as thoseselected from alkylcellulose ethers, hydroxyalkyl cellulose ethers andhydroxyalkyl alkylcellulose ethers, e.g., methylcellulose; hydroxypropylmethylcellulose (HPMC); hydroxyethyl methylcellulose (HEMC);hydroxyethyl cellulose (HEC); hydroxypropyl hydroxyethylcellulose(HPHEC) and hydroxypropylcellulose (HPC), polyoxyethylene(water-soluble, high molecule weight polymers of ethylene oxide,preferably of about 20,000 molecular weight or higher, such as POLYOXresins); natural products such as guar gum, xanthan gum and similarwater-soluble thickening agents, will serve as stabilization agents(“Stabilizers”) for the frothed Polymer dispersion. From about 0.05,preferably about 0.1, and more preferably about 0.2 percent, to about 2percent preferably to about 1, and more preferably to about 0.5 percentof stabilizer, based on the dry weight of the Polymers.

Treatment Equipment and Process Conditions

The Froth may be prepared using any suitable equipment normally employedfor frothing of aqueous liquids and dispersions and Foam of theinvention is prepared by drying of such Froth. Any mixing or stirringdevice useful for preparation of aqueous particulate dispersions can beutilized in preparation of the dispersion and in subsequent formulationand blending with surfactants and other additives, with care being takento avoid entraining significant amounts of air in the blend beforefrothing commences. A kitchen blender or other bladed mixing equipmentis such a suitable device. When the blend is prepared, the same ordifferent mixing device can then be operated to commence air entrainmentin the formulated aqueous blend containing the Polymer and otheradditives. A specifically designed frother such as a Cowie-Riding twinfoamer may be used to prepare the Froth, so that the desired target80-90 or 95 vol. % air content of the Froth, depending on the desireddensity of the final Foam, may be attained. The correct amount offrothing and air content can be easily determined by a few simpleexperiments. Froth density is measured by drawing off samples of theFroth in cups of predetermined volume and weight, weighing theFroth-filled cup and then calculating the density of the sample. Incommercial frothers, air can be added directly into the mixing head toassist in development of low density Froth. The speed of the frothingdevice can be increased or decreased to attain a desired Froth density.

Drying of the Froth to form the desired Foam of the invention may beconducted in batch or continuous mode. Devices such as conventionalforced air drying ovens or banks of infrared heating lamps or dielectricheating devices, e.g., radio (typically operated at permitted frequencybands in the range between 1-100 megaHertz) and microwave (typicallyoperated at permitted frequency bands in the range between 400 to 2500megaHertz) frequency energy generating sources, lining a tunnel orchamber in which the Froth may be placed or conveyed through, in acontinuous fashion, may suitably be employed for drying. A combinationof such drying energy sources may suitably be employed, eithersimultaneously or sequentially applied, to dry Froth to form Foam. Thesimultaneous use of a dielectric device and a forced air drying oven isa preferred mode of operation, and for Foam on the order of a quarterinch (˜0.6 cm) thickness the drying can be achieved as quickly as 45-90seconds when the forced air oven is operated at approximately 75 deg C.and a radio frequency generator heats the Froth to an internaltemperature of about 45-50 deg. C. The temperature of the Dryingoperation is selected according to the nature and the melting range ofthe Polymer (as determined by DSC) employed to prepare the Foam, asdescribed immediately below. The dielectric heating frequency bands,permitted for industrial use in various countries, are designated ingreater detail in the reference “Foundations of Industrial Applicationsof Microware and Radio Frequency Fields”, Rousy, G and Pierce, J. A.(1995).

Drying and Recovery Steps

Foam is suitably prepared by removing the liquid/aqueous element of aFroth prepared in the manner of the foregoing teaching. Desirably theamount of froth volume collapse during this conversion is to beminimized. Generally, Foams will have volume losses of not greater thanabout 30% during the drying process. The Froths are dried and convertedto invention Foams suitably by heating them in a forced air drying oven,at temperatures selected for optimum drying. Typically the Froth isheated to a temperature between about 60 and 120 deg C. (˜140 and 250deg F.). As the nature of the Polymer permits, processing is conductedat the highest temperature feasible to remove water as rapidly aspossible from the Froth without destroying the viscosity of the Polymeron the surface of the bubbles of the Froth or causing significant (e.g.,more than 30 volume percent) collapse of the partially dried froth.Typically, it is desirable to perform the drying step at a temperaturethat approaches, but does not exceed the Polymer's melting range. Thedesired condition is to attain a temperature where the amorphous regionsin the Polymer can begin to coalesce while the pseudo-crosslinkings inthe Polymer, created by the crystalline regions in same, are stillcapable of imparting sufficient viscosity to the heated Polymer to avoidor at least minimize collapse of the Froth before the Foam has becomefully “dried” in its ultimate form and dimension and at least 95 weightpercent of the water in the Froth has been driven out.

The melting range of a Polymer is determined by Differential ScanningCalorimetry (DSC) techniques, and the temperatures bracketing the regionof the DSC endotherm, or the final endotherm if more than one exist,just before a return to baseline on the DSC scan plot is the temperaturerange in which drying of the Froth to form the finished Foam is to beconducted. As described earlier the particularly preferred Polymers,when used without other polymers or additives, are characterized byexhibiting a specific desirable DSC plot of their endotherm(s).

In such Polymers, the desired endotherm exhibits a relatively gradualpositive slope as the scanning temperature is increased past the finalendotherm maximum (i.e., the last inflection point, as represented bypoint A on the curve in FIG. 1, on a DSC curve where the curve slopethen becomes positive and the curve returns to baseline state). Thisreflects a polymer of broad melting range rather than a polymer havingwhat is generally considered to be a sharp melting point. Consequently,the drying temperature for a Polymer is best maintained at or near apoint (e.g., represented by point B on FIG. 1) on the endotherm curve asignificant distance from the return to baseline position at which pointa major part, but not all, of the crystalline portions the Polymer fuseand Polymer particles fuse/coalesce. During the Drying process, bymaintaining such a temperature, most of the Polymer is allowed to fusewithout a complete loss of Polymer tensile strength and the bubblecollapse that would otherwise ensue, if all crystalline portions of thePolymer were to be melted quickly.

When Drying is to be conducted with a dielectric heating source (e.g.,microwave generator), it is desirable to ensure that the liquid used toprovide the aqueous element of a Froth contains at least a trace amountof ionic material. This can be accomplished by use of an ionicsurfactant as the Dispersant or frothing surfactant or by adding a smallamount (e.g., 100 ppm) of water soluble alkali metal electrolyte salts,such as sodium acetate, potassium bicarbonate or the like, to theDispersion prior to or during Frothing.

When a blend of Polymer with additives (including blends with otherthermoformable polymers) is to be employed in the preparation of Frothused to make the invention Foam, a DSC plot for the blend is firstsuitably generated. From that plot endotherm(s) of the blend may beobserved and, consequently, the final melting range of the blenddetermined and a suitable drying temperature for converting the Froth todurable Foam selected.

In a preferred method for making the Foam, Froth is continuouslydoctored onto a conveyor device from which the resultant Foam will berecovered. Alternatively, Froth may be doctored directly onto asubstrate to which, when dried, it will adhere to form a laminatedstructure with the resultant Foam on at least one side of thatsubstrate. If desired, a substrate may be applied to each Major Surfaceof the Froth providing a resultant Foam “sandwich”, or multiple layersof Foam, separated by one or more substrate elements may be readilyfabricated by alternating Foam/substrate/Foam/substrate, etc. As amatter of choice, either the Foam or substrate may provide the outerlayers of the laminated structure, or one outer layer of each type maybe selected, as can readily be perceived and prepared by the artisan.However, the Foam typically can be attached to a desired substrate inany conventional manner, e.g., by mechanical means, by use of adhesives,by heat lamination, etc.

In a particularly preferred method, the Froth is doctored on acontinuously moving substrate (or multiple layers ofsubstrate/Froth/substrate, etc. are laid in a continuous fashion) andthe Drying step is conducted in a continuous rather than batch fashion.More preferably the Drying step employs at least two energy sources, andwhich even more preferably are applied in a continuous fashion. Mostpreferably the at least two energy sources are configured in a manner toallow Drying to be conducted either through a simultaneous or asequential exposure of the Froth to those drying energy sources.

A particularly preferred embodiment of the invention is to continuouslydoctor Froth on a substrate, which itself has fluid absorptiveproperties and to which the Polymer in the Froth may readily bond whenheated. Drying then yields a laminated foam structure that creates acohesive structure comprising two layers of different absorbentmaterials. A laminate structure with different wicking and/or fluidabsorbent capacity properties in each laminate layer is thereby formedfrom which useful absorbent articles can be fabricated. For example apre-formed, thermoplastic polymeric foam substrate layer of desiredopen-cell structure and desired cell size may serve as such a basesubstrate. Such a substrate layer is preferably made up primarily of thesame thermoplastic material as that of which the Froth is mainlycomprised.

One means to obtain such a two-layer structure is to prepare a firstFroth, dry it into a resulting Foam and shape appropriately for use asthe first substrate layer. Then upon that first Foam substrate, lay downa second (same or different than the first) Froth of the invention anddry the second Froth to form the second Foam layer.

Alternatively, two Froths are prepared and the first Froth is preparedwith a sufficient vertical compressive strength, so that the secondFroth can be laid on top of the first Froth layer without a significantreduction in the volume of the first Froth layer.

One means to attain sufficient vertical compressive strength in thefirst Froth layer is to select a first Froth having a density greaterthan that of the second Froth layer to be laid on it. Another means toattain the desired vertical compressive strength is to partially dry theexposed major surface of the first Froth layer only enough to produce alight skin sufficient to support the weight of the second Froth layerwithout significant reduction in volume of the first Froth. Both Frothlayers are then simultaneously fully dried to Foam, resulting in a twolayer Foam laminate structure. In another variant of the invention, thefirst Foam layer is prepared from an extruded, open cell thermoplasticfoam of a material of same or similar nature compatible to that employedin forming the Froth to be laid on the first Foam. Alternatively, thefirst Foam layer is prepared from a different yet compatible type ofopen cell Foam (e.g., a polyurethane open cell foam) then a layer ofFroth (e.g., a polyolefin open cell froth) is laid upon that first Foamto yield a useful dual layer Foam structure.

In any of the structured, laminate embodiments of the invention, twodifferent layers of Foam having structures of differentiated capillaryforce, for example two different cell architectures or Foams ofdifferent average cell sizes, are preferably selected for the first andsecond Foams of a laminate structure. Because of the similar or samenature of the Polymer base in the Foam layers, a good bond is formedbetween them so that a structured laminate is formed which can exhibit aselected absorption and/or wicking property in each layer of thestructure due to the different capillary force of the Foam in eachlayer.

Foam having different cell architectures within it is one preferredembodiment of a structure exhibiting differentiated capillary forces.Such a structure provides a differentiated absorption and/or wickingcapability in distinct layers of the structure. Thepolyolefin/polyurethane dual layer Foam structure noted above, is oneexample of such a differentiated cell architecture. Another embodimentof the invention, and especially preferred, is a Foam that has a majorportion of substantially ellipsoidal cells, and having their major axisgenerally aligned in parallel fashion to a Major Surface, and lying inan xy-plane, of the Foam. Such Foam may be prepared by subjecting thedurable Foam to mild heating while uniformly applying pressure to atleast one surface of the Foam in a cell orienting fashion. Preferablythe major portion of the surface cells in the resultant Foam becomestably formed in a generally ellipsoidal shape, the major axis of suchellipsoidal cells being generally aligned with the xy-plane and roughlyparallel to a Major Surface of the Foam.

One method to achieve such ellipsoidal cell shaping and major axisorientation is to subject the durable Foam, preferably just after itsdrying, to a temperature at the lower end or at least substantiallybelow the upper end of the melting range of its component polymer(s).The Foam is heated to a temperature near the lower end of the meltingrange, providing sufficient heat to soften at least one surface of theFoam without initiating Foam collapse, while evenly and uniformlyapplying a modest pressure to that surface. Sufficient heat and pressureare applied to cause the diameter of such cells at least at and nearsuch surface to be shortened along their z-axis, thereby causing them toassume the shape of a “flattened” beach-ball and imparting anellipsoidal shape to those cells with the major (longest) axis of thethree-dimensional cell oriented generally perpendicular to the z-axisand in an xy-plane of the Foam. While cells below the surface of theFoam to which pressure and heat is applied may also be “flattened” intoellipsoids, it is not necessary to do so to more than a depth of about 2to 25 percent of the initial thickness of the Foam if the Foam isprimarily intended for use as a single layer core for both absorptionand distribution of fluid in for example a personal hygiene article;i.e., compression of the Foam need only be by about 2, preferablygreater than about 5 and more preferably greater than about 7, to lessthan 25, preferably less than about 20 and more preferably less than 15percent in thickness. Foams with such compression provide surprisinglyenhanced wicking capabilities over those which have not had asignificant percentage of their cells reoriented into the ellipsoidalstructure. If a Foam is intended primarily for use as a distributionlayer/component in an article, greater than 50 percent compression toachieve reorientation of a majority of cells into the ellipsoidal cellshape may be desirable.

In practice, for a polyethylene-based Foam later described in preferredembodiments, the reorientation of cells into ellipsoidal shape isachieved by heating at least one surface to a temperature of from about40 to about 60 deg C. while applying a suitable pressure. Such a typicalsuitable pressure (gauge) of from about 240 kPag to about 830 kPag(about 35 to about 120 psig) and preferably of between about 310 kPag toabout 620 kPag (about 45 to about 90 psig) provides a Foam withsufficient ellipsoidal cell structure at or near the surface to enhancethe vertical wicking capabilities over the same unmodified Foam severalfold and, in optimized form, such modified Foams can exhibit a verticalwicking height for 0.9% saline in excess of 8 and even of 10 cm.

While both Major Surfaces of a Foam may be treated to provideellipsoidal shaped cells it is generally sufficient, when both fluidabsorption and distribution attributes are desired in a Foam, to treatonly one Major Surface because the primary purpose is to achieve adifferentiated absorptive profile on the two opposite Major Surfaces. Itmay be advantageous to so treat both Major Surfaces simultaneously, ifafterwards the Foam will be slit longitudinally and roughly along themedian xy-plane between the two Major Surfaces of the Foam, as describedin greater detail below, to provide two “half” sheets of Foam withsimilar adsorptive profiles and cell size and architecture gradientsfrom the original Major Surface to the original center of the Foamlayer.

Other substrates with which the invention Foam may be combined to formcohesive articles are preferably made of the same polymer as mainlycomprises the Froth or one also capable of readily bonding to it.Illustrative examples of suitable substrates are woven or non-wovenfabric; loose substrate structures that are generated in a meltspun-bonding process or a similar melt blown or air laid non-wovenstructure or one generated by other similar fabrication techniques; arelatively open woven mesh; a cellulosic sheet (e.g., paper, cardboardand the like); a glass fiber insulation batting and derivative sheetarticles; thermoplastic film or sheet, such as a diaper or femininehygiene product backing sheet; a laminated metallized plastic sheet or afilm such as used to back an insulation foam material; a carpet backingfabric or mesh, and the like.

If desired, a Froth or multiple layers of Froth may be formed into ashaped profile, by forcing the Froth through a die or otherprofile-inducing shaped structure, before the drying step is performed.An embossing step may be conducted by application of shaped elements onthe conveying belt for the Froth during drying, or later in a separatethermal embossment step by application of a heated, shapedelements-bearing belt or wheel to a major surface of the Foam. Inanother embodiment, the Froth may be placed in a heated mold form inwhich channels are provided to conduct generated steam from the Foam tothe ambient atmosphere. Molded articles of Foam that have a particularlydesired shape can be formed that are then useful in the fabrication ofabsorbent articles, particularly for hygiene and medical applicationswhere body conformable articles are often desired.

Foam Slitting Step

While Foams of the invention may be utilized directly as laid and dried,particularly in commercial operations where a sheet of Froth andresultant Foam may be continuously produced, it is frequently desired toform a durable Foam of roughly twice the thickness of the Foam to beused in the finished article. Then to slit the Foam along the axis ofthe direction of continuous flow into two Foam sheets of about the samethickness.

By virtue of the fact that a foam will normally dry more quickly at itsouter, exposed surfaces than in the interior of the foam, the size ofthe open cells on the outer surfaces when dried will normally be smallerthan the size of the cells in the interior. This is a result of the factthat there will be a certain amount of bubble coalescence and resultantbubble diameter enlargement during the drying step. The size of thebubbles/final cell size is a function of time required to dry the Frothand for the Polymer particles to merge to form cell walls in the finalFoam. The longer the time, the more bubble coalescence will occur, morebubble diameter enlargement will take place and the larger will be theultimate cell size in the finished Foam. Accordingly, unless a uniformdrying throughout the Foam can be accomplished there will be some cellsize gradient from the surface to the interior of the Foam as formed.This result is desirable in many applications such as sound insulation,and in absorbent applications where the foam needs to uptake fluidquickly, yet wick fluid away from one surface of foam, e.g., in diapers,adult incontinence articles or feminine hygiene articles, as theultimate goal. After slitting of the Foam along an xy-planeapproximately midway between the Major Surfaces (or “Foam center”), theresulting two pieces of Foam will exhibit the cell size gradient fromone surface to the other in a mirrored fashion for each half of the slitFoam sheet. In use of the slit Foam for wicking applications, the Foamis oriented so that the larger cells of one Major Surface will initiallycontact the aqueous solution to be absorbed and then the capillaryaction of the increasingly smaller cells traveling toward the othermajor surface will cause the solution to be wicked away from the firstmajor surface and to be distributed nearer to the second major surface.The result is a dryer surface near the point of initial contact with theFoam, providing the desired effect in such diaper, medical and hygieneapplications of the Foam.

For use in absorbent articles, a Foam exhibiting a cell size gradientbetween the two Major Surfaces is highly desirable, larger cells at oneMajor surface allowing for a quick uptake (i.e., “acquisition”) of fluidinsults and smaller cells at the other Major Surface imparting a wickingaction to the Foam element in a final article to move fluid away fromthe insult site. Such characteristics can, in an absorbent Foam, allowthat Foam serve as both an acquisition region and a distribution regionof an absorbent core in a hygiene article, for example a diaper, andavoid the need to use two separate materials in the two regions.Suitably, the cell size gradient in the Foam is such that the majorportion of cells fall into a range from about 5, preferably from about10 microns (micrometers) at one Major Surface of slit Foam to about1000, preferably about 1100 microns at the other Major Surface. Themajor portion of cells on one Major Surface is normally found in a rangeof between about 20 to about 100 microns and the major portion of cellsat the other Major Surface to be found in the range between about 200 toabout 1000 microns; more preferably said gradient varies from cellsranging between about 30 and about 80 microns at one Major Surface andbetween about 250 and about 800 microns at the other Major Surface, andmost preferably said gradient varies from about 30 microns at one toabout 80 microns at the other Major Surface.

Cell size gradient can be influenced by faster or slower drying of theFroth, with slower drying generally resulting in a Foam of wider cellsize gradient and faster drying in one of narrower size gradient.Addition of a more effective Froth stabilizer, such as a hydroxyalkylcellulose ethers, or film-forming additive such as a styrenic latex, mayresult in a Foam with a narrower cell size gradient as well. Slitting ofthe Foam layer of a laminated—substrate/Foam/substrate—structure canyield two Foam/substrate laminates, with each laminate of a similarstructure. Other variations on this same concept can be readilyenvisioned by the skilled artisan.

Foam Cell Size and Measurement/Calculation Methods

The size of cells in the durable Foam is determined by first obtainingan image of the cells using a Scanning Electron Microscope (SEM) toprovide a black and white image of surfaces or cross sections of theFoam. The SEM image is then subjected to electronic image scanning andthe data from the scan is analyzed by SCION imagining software availablefrom SCION Corp. to provide a cell size plot for a given image area. Thedata may be graphically displayed for further analysis as a function ofdistance along a chosen axis of the B/W image from which input wascollected to visually display the structural nature of the Foam.

Hygiene Articles

In an especially preferred embodiment of the invention, the inventionFoam is employed in fabrication of the absorbent core structure ofhygiene articles; e.g., diapers, incontinent briefs, training pants,diaper holders and liners, feminine hygiene garments, and the like,designed to provide improved fit and comfort for the wearer whileadequately containing body exudates. Such an absorbent article has acontainment assembly (chassis) typically comprising a liquid pervioustopsheet and a substantially liquid impervious backsheet, and anabsorbent core associated with the two sheets. The absorbent core isdesigned so as to preferably be relatively narrow and thin in the crotchregion of the wearable article (hereafter generically referred to as“diaper”), even when the core has absorbed significant amounts ofaqueous body fluid during use. The absorbent core, accordingly, isdesigned in a manner such that fluid is substantially moved from thecrotch region to the storage regions, preferably located in a frontand/or rear waist region(s) of the article and so as to be capable ofretention of such fluid in an effective manner.

A preferred embodiment of the article according to the present inventioncomprises an absorbent core with a crotch region and one or more waistregions, which core comprises an acquisition region, a distributionregion, a storage region, and a storage/rewet barrier means, which istypically positioned on the surface of said storage region that isoriented towards the wearer and which suitably comprises an absorbentgelling material.

The topsheet of the article is suitably an apertured structure, having aliquid pervious structured carrier with an inner surface orientedtowards the interior of the article and an outer surface oriented towardthe skin of the wearer when the article is worn, where the structuredcarrier has an effective open area of at least about 12 percent and aplurality of apertures with an effective size greater than 0.1 squaremillimeter. Optionally, the outer surface of the structured carriercomprises an effective amount of a skin care composition which ispartially transferable to the wearer's skin under conditions of use.

The term “absorbent article” refers to devices which absorb and containbody exudates and, more specifically, refers to devices which are placedagainst or in proximity to the body of the wearer to absorb and containthe various exudates discharged from the body. Absorbent articlesinclude devices designed to absorb urine, which are used by incontinentpersons. Such incontinent articles include but are not limited todiapers, adult incontinent briefs, training pants, diaper holders andliners. Other absorbent articles include those designed to absorbblood-based fluids such as menses. Such sanitary hygiene articlesinclude tampons, catamenial pads, and the like. The term “disposable” isused to describe absorbent articles which are intended to be discardedafter a single use are not intended to be laundered or otherwiserestored or reused as an absorbent article. Preferably, they are capableof being recycled, composted or otherwise disposed of in anenvironmentally compatible manner. A “unitary” absorbent article refersto absorbent articles which are formed of separate parts united togetherto form a coordinated entity so that they do not require separatemanipulative parts like a separate holder and liner.

The term “absorbent core” refers to the portions (e.g., layers) of anabsorbent article whose function are to acquire, distribute, transfer,store and/or redistribute fluid. Acquisition materials include materialswhose primary function is to acquire then relinquish fluids. Suchmaterials include acquisition layers, topsheet materials, transferlayers, flow control modules, wrap tissues or nonwoven sheets designedto prevent migration of hydrogel forming polymers, etc. The term“distribution material” refers to the absorbent core material(s) whoseprimary function is to absorb and distribute/redistribute fluid topoints away from the point of initial fluid loading. The term “storagematerial” refers to the absorbent core material that retains themajority of the fluid absorbed by the article. The terms “distributionmaterial” and “storage material” are not mutually exclusive. In certainpreferred embodiments a single material, the open-cell polyolefin Foam,functions to provide fluid acquisition and distribution, and/or fluidstorage.

The term “front” refers to the portion of an article or absorbent corethat is intended to be positioned proximate the front of a wearer. Theterm “rear” refers to the portion of an article or absorbent core thatis intended to be positioned proximate the back of the wearer. Use ofthe relative term “in front of” means a position in the article or coremore toward the front of the article or core, while the term “behind”means a position in the article or core more toward the rear of thearticle or core.

The “crotch point” of an article and the article's absorbent core isdetermined by placing the article on a wearer, placing the wearer in astanding position and then placing an extensible filament around thelegs in a figure eight configuration. The point in the article and theabsorbent core corresponding to the point of intersection of thefilament is deemed to be the crotch point of the article and theabsorbent core. The crotch point is determined by placing the absorbentarticle on a wearer in the intended manner and determining where thecrossed filament would contact the article and absorbent core.

The “crotch region” of an absorbent core corresponds to 50% of theabsorbent core's total length (i.e., in the y- dimension), where thecrotch point is located in the longitudinal center of the crotch region.The crotch region is determined by first locating the crotch point ofthe absorbent core, and then measuring forward and backward a distanceof 25% of the core's total length.

The term “crotch width” refers to the width in the crotch region of theabsorbent core that is the narrowest when measured at the crotch point.When this layer consists of a plurality of discrete layers, the layerhaving the smallest width is the width of that layer, and therefore isthe crotch width of the absorbent core. If a layer is profiled in thecross (x-) dimension, the width of the layer is determined by the widthof the highest basis weight region of the profile.

The term “layers” refers to identifiable components of the absorbentstructure, and any structure referred to as a “layer” may actuallycomprise a laminate or combination of several sheets or webs of therequisite type of materials and the term “layer” includes the terms“layers” and “layered.” The term “upper” refers to the layer of theabsorbent core which is nearest to and faces the article topsheet.Conversely, the term “lower” refers to the layer of the absorbent corenearest to and facing the article backsheet. The various members,layers, and structures of absorbent articles according to the presentinvention may or may not be generally planar in nature, and may beshaped or profiled in any desired configuration.

A diaper or other wearable, absorbent article has a front waistbandregion, a back waistband region, a center region and a periphery that isdefined by the outer edge of a backsheet and which has longitudinaledges and end edges. The longitudinal axis of a diaper runs essentiallyparallel to longitudinal edges and is nominally described as alongitudinal centerline (corresponding to the y-direction or length),while the transverse axis runs essentially parallel to end edges and isnominally described as a transverse centerline (corresponding to thex-direction or width). The diaper waistband regions comprise those upperportions of the diaper, which when worn, encircle the waist of thewearer. The diaper center region is that portion between the twowaistband regions. It comprises that portion of the diaper which, whenworn, is positioned between the legs of the wearer and covers the lowertorso of the wearer. Thus, the center region defines the area of typicalliquid deposition for a wearable, disposable absorbent article.

The topsheet and backsheet can be associated together in any suitablemanner. The term “associated” encompasses configurations where atopsheet is directly joined to a backsheet by affixing the topsheetdirectly to a backsheet, as well as configurations where the topsheet isindirectly joined to a backsheet by affixing the topsheet tointermediate members which in turn are affixed to the backsheet.Preferably, the topsheet and backsheet are affixed directly to eachother by attachment means such as an adhesive, thermal bond or otherknown attachment means. For example, a uniform continuous layer ofadhesive, a patterned layer of adhesive, or an array of separate linesor spots of adhesive may be used to affix a topsheet to a backsheet. Atopsheet typically has a slightly smaller size configuration than abacksheet. However, a topsheet and backsheet can both have the same sizeconfiguration (i.e., are coextensive) such they are joined together atthe periphery of a diaper. The size of the backsheet is dictated in partby the size of the absorbent core and the exact diaper design selected.In a common embodiment, the backsheet has an hourglass-shapedconfiguration. Other configurations such as rectangular, upper case“I”-shape, etc., are also suitable.

A diaper can have elastic members that exert a contracting force on thediaper so that it configures more closely and more comfortably to thewearer. These elastic members can be assembled in a variety of wellknown configurations, such as those described generally in U.S. Pat.Nos. 3,860,003 and 4,515,595. The elastic members can be disposedadjacent the periphery of the diaper, preferably along each longitudinaledge, so that the elastic members tend to draw and hold the diaperagainst the legs of the wearer. Alternatively, the elastic members canbe disposed adjacent either or both of the end edges of a diaper toprovide a waistband as well as, or rather than, leg cuffs.

As noted above, an absorbent core may suitably, and preferably will,comprise front and rear regions, as well as a crotch region and may bedescribed as an upper case “I” configuration. These regions are definedby determining the crotch point of a core as described earlier. Inpractice, a crotch point is determined by reference to the wearer'sanatomy. A crotch point is normally depicted as located on thelongitudinal centerline of a diaper and absorbent core. This willgenerally be the case, regardless of the diaper/absorbent coreconfiguration. As noted, the crotch region may be defined by measuringboth forward and backward from the crotch point a distance, each way, of25% of the core's total length, the crotch region then being envisionedas the area enscribed between two parallel, imaginary transverse linesdrawn perpendicular to and crossing the centerline at said 25% distancepoint. Consequently, an absorbent core is considered to have a frontregion, a back region, and a crotch region. The crotch region of thecore can be used to define the corresponding crotch region of thearticle.

The topsheet is liquid pervious, permitting bodily liquids to readilypenetrate through its thickness. It is preferably compliant, softfeeling and non-irritating to the wearer's skin. A suitable topsheet maybe manufactured from a wide range of materials, such as highly porousfoams; reticulated foams; apertured plastic films; or woven or nonwovenwebs of natural fibers (e.g., wood or cotton fibers), synthetic fibers(e.g., polyester or polypropylene fibers), or a combination of naturaland synthetic fibers. A topsheet can be made of a hydrophobic materialto isolate the wearer's skin from liquids contained in the absorbentcore that is treated on at least one side with a surfactant to allowliquids to readily penetrate through its thickness.

The topsheet may comprise a structured carrier material as disclosed byRoe et al. in WO 99/25288 publication 27 May 1999 (PCT/US97/20842). Sucha structured carrier preferably has a plurality of apertures with aneffective aperture size of at least 0.2 square millimeters (mm), morepreferably of at least 0.5 square mms, even more preferably of at least1.0 square mm, and most preferably of at least 2.0 square mm. Effectiveapertures are those which have a gray level of 18 or less on a standardgray level scale of 0-255, under the image acquisition parametersdescribed in the noted Roe et al. patent publication.

The structured carrier preferably has an effective open area of at least15 percent, more preferably of at least 20 percent, even more preferablyof at least 25 percent, and most preferably the structured carrier hasan effective open area of at least 30 percent. Carriers so constructedare particularly effective in receiving fecal matter.

At least a portion of the topsheet can be subjected to mechanicalstretching in order to provide a “zero strain” stretch laminate thatforms the elastic side panels. To achieve this, the topsheet ispreferably elongatable, most preferably drawable, but not necessarilyelastomeric, so that the topsheet will, upon mechanical stretching, beat least to a degree permanently elongated such that it will not fullyreturn to its original configuration. The topsheet can be subjected tomechanical stretching without undue rupturing or tearing of thetopsheet, for which it is preferred that the topsheet have a lowcross-machine direction (lateral direction) yield strength.

There are a number of manufacturing techniques which may be used tomanufacture a topsheet. For example, the topsheet may be a nonwoven webof fibers. When a topsheet comprises a nonwoven web, the web may bespunbonded, carded, wet laid, meltblown, hydroentangled, combinations ofthe above, or the like. A preferred topsheet is carded and thermallybonded by means well known to those skilled in the fabrics art. Apreferred topsheet comprises staple length polypropylene fibers having adenier of about 2.2. By the term “staple length fibers” we refer tofibers having a length of at least about 15.9 mm (0.625 in). Preferably,the topsheet has a basis weight from about 18 to about 25 g/m². Asuitable topsheet has been offered by International Paper Company,Veratec division, Walpole, Mass., under the designation P-8.

A topsheet is positioned above the body surface of an absorbent core. Inpreferred embodiments, an acquisition material is positioned between anabsorbent core and a topsheet. The topsheet can be joined to theabsorbent core and/or backsheet by suitable attachment means, well knownin the art. Suitable attachment means are described below with respectto joining a topsheet and/or a backsheet to an absorbent core.

The term “joined”, as used here, encompasses configurations where anelement is directly secured to another element by affixing the firstelement directly to the second, and configurations whereby the firstelement is indirectly secured to the second by affixing the element tointermediate member(s) which in turn are affixed to the other element.In a preferred embodiment, a topsheet and a backsheet are joineddirectly to each other at the diaper periphery. They can also beindirectly joined together by directly joining them to an absorbent coreby suitable means. In an alternative embodiment, the absorbent core (oracquisition material) need not be joined to either the topsheet or thebacksheet, so the absorbent core is allowed to “float” between them. Theacquisition material is preferably in fluid communication with andassociated with, and more preferably an integrated portion of, theabsorbent core.

The backsheet is substantially impervious to liquids (e.g., urine) andis preferably manufactured from a thin plastic film, although otherflexible liquid impervious materials may also be used. The term“flexible” refers to materials which are compliant and will readilyconform to the general shape and contours of the wearer. A backsheet isintended to prevent exudates, absorbed and contained in the absorbentcore, from soiling or wetting articles which contact the outer diapersurface. A backsheet may thus comprise a woven or nonwoven material,polymeric films, e.g., thermoplastic films of polyethylene orpolypropylene, or composite materials, e.g., a film-coated nonwovenmaterial. Preferably, the backsheet is a thermoplastic film of athickness from about 0.012 mm (0.5 mils) to about 0.051 mm (2.0 mils).

In a preferred embodiment of the invention, at least a portion of thebacksheet is subjected to mechanical stretching in order to provide botha “zero strain” stretch laminate that forms the elastic side panels and,if desired, to prestrain the portion of the backsheet coinciding withthe elastic waist feature or any other elastic feature. For this, thebacksheet is preferably elongatable, most preferably drawable, but notnecessarily elastomeric, so that the backsheet will, upon mechanicalstretching, be at least to a degree permanently elongated and will notfully return to its original undistorted configuration. In preferredembodiments, the backsheet can be subjected to mechanical stretchingwithout undue rupturing or tearing. It is preferred that the backsheethave an ultimate elongation to break of at least about 400% to about700% in the cross-machine direction, as measured using a methodconsistent with ASTM D-638. Preferred polymeric films for use as such abacksheet contain a high content of linear low density polyethylene, forexample DOWLEX resin from The Dow Chemical Company, Midland, Mich.Particularly preferred materials for the backsheet include blendscomprised of about 45-90% linear low density polyethylene and about10-55% polypropylene. Exemplary films for use as the backsheet of theinvention are offered by Tredegar Industries, Inc. of Terre Haute, Ind.under the designations X-8323 film, RR8220 blend for certain blownfilms, and RR5475 blend for certain cast films.

The backsheet can be embossed (typically, to a caliper of about 0.127 mm(5.5 mils)) and/or matte finished to provide a more clothlikeappearance. The backsheet may permit vapors to escape from the absorbentcore (i.e., breathable) while still preventing exudates from passingthrough the backsheet. Examples of vapor permeable backsheet materialsinclude microporous films, such as available from ExxonMobil Chemicalunder the designation EXXAIRE film, or laminated, monolithic films, suchas available from Elf AtoChem under the designation PEEBAX, or fromDuPont under the designation HYTREL.

A backsheet is positioned adjacent the lower surface of the absorbentcore and can be joined to it by art-known attachment techniques.Alternatively, an additional material (e.g., additional storage oracquisition material) may be placed between the backsheet and theabsorbent core. For example, the backsheet may be secured to theabsorbent core or any intervening material by a uniform continuous layerof adhesive, a patterned layer of adhesive, or an array of separatelines, spirals, or spots of adhesive. Adhesives which have been found tobe satisfactory are manufactured by Century Adhesives, Inc. of Columbus,Ohio and marketed as Century 5227 and by H. B. Fuller Co. of St. Paul,Minn. and marketed as HL-1258. The attachment means preferably comprisesan open pattern network of filaments of adhesive as described in U.S.Pat. No. 4,573,986. Exemplary attachment means are illustrated by theapparatus and methods shown in U.S. Pat. Nos. 3,911,173; 4,785,996; and4,842,666. Also, the attachment means may comprise heat bonds, pressurebonds, ultrasonic bonds, dynamic mechanical bonds, or any other suitableattachment means or combinations of same.

The absorbent core comprises absorbent material, at least one of whichcomprises the Foam of the invention, and is capable of acquiring,distributing and/or retaining liquids such as urine and certain otherbody exudates, in suitable manner and degree.

The storage region in the absorbent article comprises a Foam of theinvention, high surface area fibers, hydrogel forming materials orcombinations thereof, or other high capacity absorbent material that hasgood retention properties for the bodily fluids to be captured.

Acquisition Material

In addition to or in place of the Foam of the invention, hydrophilicfibers may be employed as the acquisition material. Particularlysuitable for this purpose is chemically stiffened cellulosic fibers. Weuse the term “chemically stiffened cellulosic fibers” to mean cellulosicfibers that have been stiffened by chemical means to increase thestiffness of the fibers under both dry and wet conditions. Such meansinclude the addition of a chemical stiffening agent that, for example,coats and/or impregnates the fibers. Such means can include thestiffening of the fibers by altering the chemical structure, e.g., bycross-linking polymer chains.

Polymeric stiffening agents that can coat or impregnate the cellulosicfibers include: cationic modified starches having nitrogen-containinggroups (e.g., amino groups), latexes; wet strength resins such aspolyamide-epichlorohydrin resin; polyacrylamide resins described, forexample, in U.S. Pat. No. 3,556,932 and commercially availablepolyacrylamides marketed by American Cyanamid Co., Stamford, Conn.,under the tradename Parez 631 NC; urea formaldehyde and melamineformaldehyde resins; and polyethylenimine resins. A general dissertationon wet strength resins utilized in the paper art, and generallyapplicable here, can be found in TAPPI monograph series No. 29. “WetStrength in Paper and Paperboard”, Technical Association of the Pulp andPaper Industry (New York, 1965).

Fibers can also be stiffened by chemical reaction. For example,crosslinking agents can be applied to the fibers that, subsequent toapplication, are caused to chemically form intrafiber crosslink bonds.Such bonds can increase the stiffness of the fibers. While utilizationof intrafiber crosslink bonds to chemically stiffen the fiber ispreferred, it is not meant to exclude other types of reactions forchemical stiffening of the fibers.

In the more preferred stiffened fibers, chemical processing includesintrafiber crosslinking with crosslinking agents while such fibers arein a relatively dehydrated, defibrated (i.e., individualized), twisted,curled condition. Suitable chemical stiffening agents are typicallymonomeric crosslinking agents including, but not limited to, C₂-C₈dialdehyde, C₂-C₈ mono-aldehydes having an acid functionality, andespecially C₂-C₉ polycarboxylic acids. These compounds are capable ofreacting with at least two hydroxyl groups in a single cellulose chainor on proximately located cellulose chains in a single fiber. Specificexamples of such crosslinking agents include, but are not limited to,glutaraldehyde, glyoxal, formaldehyde, glyoxylic acid, oxydisuccinicacid and citric acid. The effect of crosslinking under these conditionsis to form fibers that are stiffened and which tend to retain theirtwisted, curled configuration during use.

The chemically stiffened cellulosic fibers have certain properties thatmake them particularly useful in certain absorbent members in theinvention, relative to unstiffened cellulosic fibers. In addition tobeing hydrophilic, the stiffened fibers have unique combinations ofstiffness and resiliency. This allows thermally bonded absorbentstructures made with such fibers to maintain high levels of absorptivecapacity, and to exhibit high levels of resiliency and an expansionaryresponsiveness to wetting. The resiliency of such stiffened fibersenables an absorbent member to better maintain its capillary structurein the presence of both fluid and compressive forces normallyencountered during use and are thus more resistant to collapse. Fibersstiffened by crosslink bonds and processes for their preparation, aredisclosed, in U.S. Pat. Nos. 3,224,926; 3,440,135; 3,932,209; and4,035,147. Preferred stiffened fibers are disclosed in U.S. Pat. Nos.4,822,453; 4,888,093; 4,898,642; and 5,137,537, all incorporated here byreference.

Distribution Material

As discussed, the absorbent core comprises a material which functions todistribute fluid out of the core's crotch region. The distributionmaterial will frequently be utilized in absorbent articles in a mannersuch that fluid to be absorbed must be moved within the article from arelatively lower to a relatively higher position, with respect togravitational force, within the absorbent core of the article.Accordingly, the ability of the distribution materials to wick fluidagainst gravitational force is particularly relevant to theirfunctioning as absorbent materials in the present absorbent articles.Vertical wicking, i.e., fluid wicking in a direction opposite fromgravitational force, as measured in the test described below, is anespecially desirable performance attribute for the distributionmaterial.

The Foam of the invention has particularly good vertical wickingproperties and is preferred for use as the distribution material,especially when integration of the Acquisition and Distribution materialare consolidated and provided in a single material, rather than providedas separate regions of different materials. However, other material thatfunctions as an efficient distribution material may be employed inconjunction with or in place of the invention Foam. Wickingcharacteristics that are particularly relevant for fluid distributionare: A) the rate of vertical wicking of fluid through the distributionmaterial; and B) the absorbent capacity of the distribution material atspecific referenced wicking heights. Another important property ofdistribution material is its ability to drain (partition) fluid fromcompeting absorbent structures (e.g., acquisition materials) with whichthe material can be in contact.

Consequently, any material that substantially meets the above notedcriteria may be used as a distribution material. In addition to the useof a Foam of the invention, fluid distribution members may benefit fromthe integration of a thermally bonded polymer micro-web in the material.This micro-web is formed by the polymer bonding fibers (such asHoechst-Celanese Copolyolefin Bicomponent fiber and the like) stronglybonding at fiber intersections. In these embodiments, the thermoplasticbinding material provides bond sites at intersections of the bindingfibers with either other binding fibers, chemically stiffened, twisted,and curled cellulosic fibers, or high surface area fibers such as thosenoted as useful in the Acquisition Material section, above. Suchthermally bonded webs are, in general, made by forming a web comprisingthe stiffened cellulosic fibers and thermoplastic fibers, preferablyevenly distributed throughout. The thermoplastic fibrous material issuitably intermixed with the stiffened cellulosic fibers and fine fibersin an aqueous slurry prior to web formation. The web, once formed, isthermally bonded by heating the web until the thermoplastic portion ofthe fibers melt. Specific non-limiting examples of suitable fibrousmaterials include polyester hot melt fibers (KODEL 410), bicomponentfibers, tricomponent fibers, mixtures thereof, and the like.

Suitable fibrous fluid distribution materials as described above can befurther modified by being mechanically treated, as described in EuropeanPatent publication-A-0.810.078, incorporated specifically here byreference.

Storage Materials

Suitable material for use in the storage region of the absorbent core ofthe articles are the invention Foam having an average cell size at thelarge end of the average cell size range previously taught, above. Alsouseful for this purpose are polymeric foams having a relatively highFree Absorption Capacity.

In those embodiments where the distribution material is not particularlysuitable for storage of absorbed fluids, the absorbent core alsocomprises a material, or combination of materials, whose primaryfunction is the storage of absorbed fluids. Such a fluid storagematerial acts to store body exudates away from the wearer's body, toleave the wearer with a feeling of dryness. The storage materials aremaintained in fluid contact with the distribution material so that urineor other aqueous body fluids absorbed by the distribution material canbe desorbed by the fluid storage material. When storage materials arepositioned in the front and/or rear regions of the absorbent core, thecore provides comfort benefits by storing a majority of the absorbedfluid away from the article's crotch region.

Any material capable of partitioning fluid from the distributionmaterial may be utilized as the storage material. For example, a storagematerial may comprise hydrogel-forming polymers that arewater-insoluble, but water-swellable and are capable of absorbing largequantities of fluids. Such polymers are commonly referred to as“hydrocolloids” or “superabsorbent” materials, and includepolysaccharides such as carboxymethyl starch, carboxymethyl cellulose,and hydroxypropyl cellulose; nonionic types such as polyvinyl alcohol,and polyvinyl ethers; cationic types such as polyvinyl pyridine,polyvinyl morpholinione, and N,N-dimethylaminoethyl orN,N-diethylamino-propyl acrylates and methacrylates, and theirrespective quaternary salts. Typically, useful hydrogel-formingabsorbent polymers have a multiplicity of anionic functional groups,such as sulfonic acid, and more typically carboxy groups. Examples ofpolymers suitable for such use include those which are prepared frompolymerizable, unsaturated, acid-containing monomers. Such monomersinclude the olefinically unsaturated acids and anhydrides that containat least one carbon to carbon olefinic double bond. More specifically,these monomers can be selected from olefinically unsaturated carboxylicacids and acid anhydrides, olefinically unsaturated sulfonic acids, andmixtures thereof.

Some non-acid monomers can also be included, usually in minor amounts,in preparing the hydrogel-forming absorbent polymers. Such non-acidmonomers can include, for example, the water-soluble orwater-dispersible esters of the acid-containing monomers, as well asmonomers that contain no carboxylic or sulfonic acid groups at all.Optional non-acid monomers can thus include monomers containing thefollowing types of functional groups: carboxylic acid or sulfonic acidesters, hydroxyl groups, amide-groups, amino groups, nitrile groups,quaternary ammonium salt groups, aryl groups (e.g., phenyl groups, suchas those derived from styrene monomer). These non-acid monomers arewell-known materials and are described in greater detail, for example inU.S. Pat. Nos. 4,076,663 and 4,062,817, both of which are hereincorporated by reference.

Olefinically unsaturated carboxylic acid and carboxylic acid anhydridemonomers include the acrylic acids typified by acrylic acid itself,methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylicacid, β-methacrylic acid (crotonic acid), α-phenylacrylic acid,β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelicacid, cinnamic acid, p-chlorocinnamic acid, β-sterylacrylic acid,itaconic acid, citroconic acid, mesaconic acid, glutaconic acid,aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleicacid anhydride.

Preferred hydrogel-forming absorbent polymers for use in the presentinvention contain carboxy groups. These polymers include hydrolyzedstarch-acrylonitrile graft copolymers, partially neutralized hydrolyzedstarch-acrylonitrile graft copolymers, starch-acrylic acid graftcopolymers, partially neutralized starch-acrylic acid graft copolymers,saponified vinyl acetate-acrylic ester copolymers, hydrolyzedacrylonitrile or acrylamide copolymers, slightly network crosslinkedpolymers of any of the foregoing copolymers, partially neutralizedpolyacrylic acid, and slightly network crosslinked polymers of partiallyneutralized polyacrylic acid. These polymers can be used either solelyor in the form of a mixture of two or more different polymers. Examplesof these polymer materials are disclosed in U.S. Pat. Nos. 3,661,875;4,076,663; 4,093,776; 4,666,983; and 4,734,478, and are hereincorporated by reference.

Preferred hydrogel-forming polymer materials are slightly networkcrosslinked polymers of partially neutralized polyacrylic acids andstarch derivatives of same. More preferably, the hydrogel-formingabsorbent polymers comprise from about 50 to about 95%, preferably about75%, neutralized, slightly network crosslinked, polyacrylic acid (i.e.poly (sodium acrylate/acrylic acid)). Network crosslinking renders thepolymer substantially water-insoluble and, in part, determines theabsorptive capacity and extractable polymer content characteristics ofthe hydrogel-forming absorbent polymers. Processes for networkcrosslinking such polymers are described in greater detail in U.S. Pat.No. 4,076,663.

Hydrogel-forming polymers are optionally combined with fibrous materialsto form the storage material. The fibrous materials facilitate, interalia, uptake of fluid by the hydrogel-forming polymer. However, it maybe preferred to use relatively high concentrations of hydrogel-formingpolymer, while at the same time avoid the gel blocking phenomenaexhibited by many hydrogel-forming polymers. The use of highconcentration hydrogel-forming polymers is described in detail in U.S.Pat. Nos. 5,599,335 and 5,562,646, both incorporated here by reference.Storage materials comprising hydrogel-forming polymers can also comprisefibrous materials to form fibrous web or fibrous matrices. Fibers usefulherein include those that are naturally occurring fibers (modified orunmodified), as well as synthetically made fibers. Examples of suitableunmodified/modified naturally occurring fibers include cotton, Espartograss, bagasse, kemp, flax, silk, wool, wood pulp, chemically modifiedwood pulp, jute, rayon, ethyl cellulose, and cellulose acetate. Suitablesynthetic fibers can be made from polyvinyl chloride, polyvinylfluoride, polytetra-fluoroethylene, polyvinylidene chloride,polyacrylics such as ORLON, polyvinyl acetate, polyethylvinyl acetate,non-soluble or soluble polyvinyl alcohol, polyolefins such aspolyethylene (e.g., PULPEX) and polypropylene, polyamides such as nylon,polyesters such as DACRON or KODEL, polyurethanes, polystyrenes, and thelike. The fibers used can comprise solely naturally occurring fibers,solely, synthetic fibers, or any compatible combination of naturallyoccurring and synthetic fibers.

The fibers used can be hydrophilic, hydrophobic or can be a combinationof both hydrophilic and hydrophobic fibers. The term “hydrophilic”describes fibers, or surfaces of fibers, that are wettable by aqueousfluids (e.g., aqueous body fluids) deposited on these fibers.Hydrophilicity and wettability are typically defined in terms of contactangle and the surface tension of the fluids and solids involved. This isdiscussed in detail in the American Chemical Society publicationentitled Contact Angle, Wettability and Adhesion, edited by Robert F.Gould (Copyright 1964). A fiber, or surface of a fiber, is said to bewetted by a fluid (i.e., hydrophilic) when either the contact anglebetween the fluid and the fiber, or its surface, is less than 90°, orwhen the fluid tends to spread spontaneously across the surface of thefiber, both conditions normally co-existing. Conversely, a fiber orsurface is considered to be hydrophobic if the contact angle is greaterthan 90° and the fluid does not spread spontaneously across the surfaceof the fiber.

For storage materials useful in the articles of the invention,hydrophilic fibers are preferred. Suitable hydrophilic fibers for use inthe present invention include cellulosic fibers, modified cellulosicfibers, rayon, polyester fibers such as polyethylene terephthalate(e.g., DACRON), hydrophilic nylon (HYDROFIL), and the like. Suitablehydrophilic fibers can also be obtained by hydrophilizing hydrophobicfibers, such as surfactant-treated or silica-treated thermoplasticfibers derived from, for example, polyolefins such as polyethylene orpolypropylene, polyacrylics, polyamides, polystyrenes, polyurethanes andthe like. For reasons of availability and cost, cellulosic fibers, inparticular wood pulp fibers, are preferred for use in the presentinvention.

Suitable wood pulp fibers can be obtained from well-known chemicalprocesses such as the Kraft and sulfite processes. It is especiallypreferred to derive these wood pulp fibers from soft woods due to theirpremium absorbency characteristics. However, as indicated, a singlematerial may function as both the distribution and storage material inthe present articles.

The crotch width of the absorbent core at the crotch point, when dry andwhen wet, is important in providing improved fit on the wearer. It ispreferred that the crotch width be small, even when wetted with fluid,so that the absorbent core undergoes minimal bunching when the wearer'slegs are closed. In this regard, absorbent cores useful in the presentinvention will have a crotch width when dry and optionally when wet ofnot more than about 9 cm. Preferably, the crotch width when dry andpreferably also when wet will be not more than about 7 cm, still morepreferably not more than about 5 cm, and yet more preferably less than 3cm. Wet crotch width can be measured following the Curved AcquisitionTest Method described in U.S. Pat. No. 6,713,661 B1 to Arndt et al. Asit pertains to the issue of bunching during wear, crotch width may bemore relevant than cross sectional area at the core's crotch point. Inthis context, the narrowest dimension in the transverse dimension isconsidered to be the crotch width layer.

As the noted tests are described in the Test Method section of the Arndtet al. '661B1 patent, preferably the absorbent article has an Actual WetCrotch Caliper (AWCC) of less than about 20 mm, more preferably lessthan 15 mm, even more preferably less than 10 mm, and most preferablyless than 5 mm. The absorbent article preferably has an AWCC of lessthan 90% of the article's Saturated Crotch Caliper (SCC) value, morepreferably less than 50%, even more preferably less than 25%. The crotchwidth of absorbent articles according to the present invention ispreferably less than about 90 mm, more preferably less than 70 mm, evenmore preferably less than 50 mm. Preferably, the article according tothe present invention Dry Crotch Caliper of less than 8 mm, morepreferably less than 5 mm, and even more preferably less than 3 mm.

It is intended that our invention provide absorbent articles that arethin in the crotch when dry, preferably less than 10 mm, more preferablyless than 8 mm, most preferably less than 5 mm. It is desired that thepresent invention provide absorbent articles with an AWCC, as determinedfollowing the Curved Acquisition Test Method, that preferably is lessthan 20 mm, more preferably less than 15 mm, even more preferably lessthan 10 mm, and still more preferably less than 5 mm. To further enhanceoverall fit and comfort of the article it is preferred that the AWCC ofthe absorbent article is less than the SCC, of the article. The SCCreflects the core condition when loaded with a relatively large gush. Inthis state, the material swells to absorb the liquid. Then, as thematerial is dewatered, the capillary forces within the structure causethe structure to recollapse providing a lower caliper AWCC than the SCC.It is preferred that the AWCC of the absorbent article be less than 90%of the SCC, more preferably less than 50%, even more preferably lessthan 25%. It is further desired that the AWCC also be less than thecaliper of the absorbent article in either one or both of the waistregions when measured immediately adjacent said crotch region, all testsas detailed in the Test Methods section of the noted '661 B1 patent.

When submitting the articles according to the present invention to theCurved Acquisition test described in the Test Method section of theArndt et al. '661B1 patent, they exhibit an initial acquisition ratepreferably of at least 5 ml/sec, more preferably of at least 10 ml/sec,even more preferably greater than 15 ml/sec, or a 4^(th) gushacquisition rate preferably of at least 0.25 ml/sec, more preferably atleast 0.50 ml/sec, and even more preferably at least 1.0 ml/sec.

When submitting articles of the present invention to the Post CurvedAcquisition Collagen Rewet test described in the Test Method section ofthe Arndt et al. '661B1 patent, they preferably exhibit a value of lessthan 150 mg, more preferably less than 100 mg, and even more preferablyless than 50 mg. These values apply for absorbent cores of 90 mm orwider width crotch upon which the 90 mm diameter test apparatus can beapplied. For absorbent cores with more narrow crotch width, a reductionin diameter of the test apparatus to match the crotch width is requiredand a reduction in the weight applied is also necessary to maintain anequal pressure per unit area for the different measurements. Forarticles comprising a rewet barrier, the Post Curved AcquisitionCollagen Rewet is preferably less than the Post Curved AcquisitionCollagen Rewet of the absorbent article where said rewet barrier regionis removed. Preferred materials for the rewet barrier are superabsorbentgelling materials, hydrogels, or superabsorbents; polymeric foammaterial or combinations thereof.

Absorbent articles according to the present invention can comprise anacquisition region which preferably comprises a material, which has aMedium Desorption Pressure (MDP) value described in the Test Methodsection of the Arndt et al. '661B1 patent, preferably corresponding to aheight of less than 15 cm, more preferably less than 12 cm, even morepreferably less than 10 cm, and preferably of more than 5 cm.

The absorbent core structure fabricated from Foam of the invention isintended to move the fluid deposited in the crotch region away from thatregion rapidly. This is reflected in the reduced level of fluid storagein the crotch region of the absorbent core. In a preferred embodiment ofthe invention, the crotch region of the absorbent core will comprisematerial(s) that function first to absorb and then to distribute fluidsaway from the crotch region. While fluid distribution is an importantfunction of the core's crotch region material, it is still within thescope of the invention to include material in the crotch region whoseprimary function is the storage of fluids, so long as the level ofstorage in the crotch region is not excessive.

Foam of the invention reduces width in the crotch region and improvesoverall absorption performance of diapers and diaper-like, wearablehygiene articles by providing an absorbent core material that is moreefficient in acquisition, and distribution of bodily liquids with whichthe core is contacted during use.

In combination with requisite crotch width parameters, the preferredabsorbent articles comprise an absorbent core that retains preferablyless than about 40% of the absorbent core's total capacity in the crotchregion of the core. The storage of smaller amounts of fluids in the corecrotch region, relative to the front/rear waist regions of the core, isa reflection of the ability of the core materials to move fluid out ofthe crotch region during wear, thereby to improve fit and wearercomfort. Absorbent cores useful in the invention more preferably retainless than about 25%, even more preferably less than about 15%, stillmore preferably from about 0% to about 10%, of the core's total capacityat equilibrium in the core's crotch region.

In certain preferred embodiments, the absorbent core is constructed suchthat a major portion of the absorbed fluid ultimately is stored behindthe crotch point of the core. Preferably at least 55%, more preferablyat least 65% and still more preferably at lest 80% of the absorbentcore's total absorbent capacity is located behind the core's crotchpoint. A method for determining total core absorbent capacity andpercent capacity of the core crotch region is described in the TestMethods section of U.S. Pat. No. 6,713,661 B1, previously noted, whichis incorporated here by reference.

In addition to crotch width and liquid storage in the crotch, anotherkey factor contributing to comfort and fit is thickness or bulk of theabsorbent core itself. It is desirable for the present invention toprovide an absorbent structure that is thin when dry, preferably lessthan about 8 mm, more preferably less than 5 mm and even more preferablyless than 3 mm, and also relatively thin when wet, preferably less than20 mm, more preferably less than 15 mm, still more preferably less than10 mm and even more preferably less than 5 mm, in each case whenmeasured at the crotch point. It is also desirable that the caliper ofthe wet absorbent article at the crotch point preferably be less thanthe caliper of the wet article measured in the front or rear waistregions immediately adjacent said crotch region.

In a preferred embodiment, the storage region can comprise two separatedsubregions positioned longitudinally offset from each other. Preferably,the crotch region of the absorbent article has an ultimate storagecapacity of less than about 40% of the total ultimate storage capacityof the absorbent core, preferably less than 25%, more preferably lessthan 10%. The relative percentage of storage in the absorbent core canbe simply determined by fully saturating the absorbent core with the0.9% saline solution, removing the core from the diaper, weighing it andthen cutting the core into its respective regions and weighing themindividually, while still saturated, using the same equipment as usedfor saturating a diaper when performing the Curve Acquisition testmethod, noted above.

A further preferred article according to the present invention comprisesa moisture vapor permeable backsheet. Such an article can comprise anabsorbent core which covers a surface area that is less than 60% of thesurface area of the moisture vapor permeable backsheet in the crotchregion, preferably less than 50%, more preferably less than 25%. Themoisture vapor permeable backsheet can comprise microporous films orlaminates, nonwovens, monolithic films or combinations thereof, such aslaminates.

In a further preferred article embodiment of the invention, theacquisition region and the distribution region of the absorbent core arecomprised of the invention Foam, and in an even more preferredembodiment, a single layer of Foam having a cell size gradient betweenone Major Surface and the opposite Major Surface of that layer serves asboth the acquisition and the distribution region of said absorbent core.

Testing Procedures

Unless otherwise indicated, the following test procedures are employedto measure the characteristics/performance of the Foam samples.

Vertical Wicking Height (“VWH”) of Foam.

This test is employed to quantify the ability of an open cell to movefluid away from the insult site (i.e., the point of contact by the“insult” fluid to be wicked away). A sample strip of the Foam,approximately 2.54 cm (˜1 inch) wide and approximately 30.5 cm (˜12inches) long is adhered to a plastic plate using double-sided tape andpositioned adjacent and parallel, in the longer direction, to a ruler orother similar measurement tool such that the bottom of the strip ispositioned with the 0 indicator marker on the ruler. The plate withsample is then suspended over a bath of the 0.9% aqueous saline solutionthat contains a minimal amount of a food coloring (to assist observationof the movement of the fluid front in the foam strip). At time “zero”the bath is raised to just contact the bottom edge of the Foam strip.The height from the bottom edge of the strip, of the fluid front on thestrip surface is recorded at selected time intervals, generally at 2, 5,10, 30 and 60 minutes. For speed and simplicity, VWH after 5 minutes isoften measured and reported. In some cases, when the sample strip isless than 30 cm, wicking may exceed the height of the strip. In suchcases, the length of the strip is indicated followed by a “+” toindicate that the VWH exceeds the height of the sample.

Absorbency Capacity (“AC”)

Absorbency capacity is determined using a pre-weighed (dry weight) foamsample. The sample is fully immersed in a bath of the same 0.9% aqueoustest solution. Once fully saturated, it's removed from the bath withtweezers or a spatula. It is placed on a coarse wire mesh where excessfluid is permitted to drain until visible fluid flow from the sampleceases and the saturated Foam sample is weighed to establish the “wetweight”. AC is then calculated by dividing the [wet weight—dry weight]difference by dry weight of the strip.

SPECIFIC EMBODIMENTS OF THE INVENTION

All reported percentages are by weight, unless otherwise stated.

Table 1 summarizes the composition and properties of various ethylenecopolymers that are useful for preparation of Froth and Foam.Exemplification of ethylene/1-octene and ethylene/1-butene copolymers isdescribed. Examples 1 through 5 demonstrate the dispersion of thePolymer, frothing of the Polymer dispersion, drying of the Froth to formthe durable Foam and the ability of the Foam to absorb and wick salineaqueous solutions (e.g. synthetic urine or synthetic blood samples, or“insults”).

TABLE 1 Polymer Composition Melt Index Ethylene/1-Octene ASTM D1283Polymer Content (* other) Density [190 deg C./2.16 kg] Designation (wt%) (g/cc) (g/10 min) 1A 55/45 0.857 1 1B 58/42 0.864 13 1C 60/40 0.87030 1D 62/38 0.870 5 1E 65/35 0.875 3 1F 67/33 0.880 18 1G 69/31 0.885 301H 78/22 0.902 30 1J 80/20 0.902 3 1K   70/30 * 0.865 5 *(Ethylene/1-Butene)

EXAMPLE 1 Dispersion

A dispersion of an ethylene/1-octene copolymer is prepared from Polymer1D (Table I above), a copolymer having ethylene/1-octene content of62/38 percent (ENGAGE 8200 elastomer which is supplied by DuPont DowElastomers), and having a density of 0.870 g/cc and a melt index of 5g/10 min (as determined by ASTM method D1238 condition 190 deg C./2.16kg). In the manner described earlier under the heading “DispersionStep”, 10,000 parts of the copolymer is fed into the hopper of thepolymer extruder together with 640 parts (active weight) of dispersant(Unicid 350, a dispersant containing a 26 carbon chain fatty acid asactive component) and melt-kneaded by a single screw extruder at about220 deg C. (˜430 deg F.). Thereafter into the barrel of the twin-screwextruder 70 parts potassium hydroxide in 850 parts deionized water areadded to the polymer/dispersant blend under pressure and a temperatureof about 165 deg C. (˜330 deg F.). As the blend passes down the extruderbarrel, further deionized water is added until a final dispersion ofabout 59% solids is produced. The resulting dispersion is cooled toabout 94 deg C. (˜200 deg F.) before exiting the extruder and thenrecovered.

Froth Preparation

A sample of 196.5 parts of the above-described dispersion (51% active or100 parts solid Polymer) is blended, in a conventional mixing bowl andtaking care not to entrain air while blending, with 3.25 parts of a 30%solution (0.98 part active) of the selected frothing surfactant (sodiumlauryl sulfate) and with 8 parts (0.33 part active) of a 2.5% aqueoussolution of the hydroxyalkyl cellulose ether Methocel E4M hydroxypropylmethylcellulose thickener supplied by The Dow Chemical Company, into 100parts deionized water. Small froth samples are prepared with aKitchenAid Professional 9-speed hand mixer (Model KMH9PWH) and largersamples are prepared with a Hobart-type stand mixer KitchenAidProfessional mixer (Model KSM50PWH) and a pair of wire beaters.

After the initial blend is prepared, air is entrained by mechanicalfrothing using the same mixers, but fitted with a wire whip and byincreasing the mixer speed from medium to high over a period ofapproximately 5 to 10 minutes, until a stiff froth is formed. Density ofthe froth is measured by weighing a 3 oz (89 ml) paper cup filled withfoam. Once the desired density is reached, whipping is stopped.

Foam Preparation/Drying

Froth prepared as described above is spread on release paper supportedby a stiffer web sheet and is smoothed to a height of about 0.25 in(˜6.4 mm) or as desired. The froth is placed in a Blue M forced air ovenat drying temperature of approximately 60 to 74 deg C. (˜140 to 165 degF.) for about 65 minutes. The dry foam sheet is recovered and slitlengthwise along the axis that parallels the two major surfaces to yieldtwo mirror image sheets of foam having small cell sizes ranging fromabout 30 to 100 microns on their outer surfaces and larger cell sizeranging from about 250 to 800 microns on their inner major surfaces.

EXAMPLE 2

In the manner described in Example 1 above, dispersions, froths and foamsamples are prepared. The types and characteristics of the Polymer aredescribed in Table 1 above. The froth stabilizer, any additive andsurfactants, the composition of the dispersions and the properties ofthe Foams are described in the following Tables 2 and 3. The Polymer isselected from a broad series of ENGAGE elastomer (ethylene/1-octenecopolymer resin), a product available from DuPont Dow Elastomers, or ananalogous copolymer from the same source with 1-butene substituted for1-octene. Unicid 350 dispersant is a 26 carbon (average chain length)fatty acid. Unicid 425 dispersant is a 32 carbon (average chain length)fatty acid. The fatty acids are utilized in their potassium salt asformed in the extrusion step described above. Frothing surfactantStanfax 318 surfactant is sodium sulfosuccinimate and Steol CS-130 is asodium long chain alkyl ether sulfate. The last two surfactants, whenutilized, are added with dilution water near point of exit of the meltfrom extruder in the extrusion step described above.

TABLE 2 Polymer Dispersion Characteristics Polymer Polymer Dispersant &Content Particle Melting Dispersion (wt % based) (wt % Size Temp. RangeDesignation (on total solids) solids) (microns) (deg C.) 2.1 6% Unicid425 1A 60.2% 1.56 25-60 2.2 6% Unicid 425 1E 54.5% 1.69 30-90 2.3 6%Unicid 425 1J 53.9% 1.18  65-110 2.4 6% Unicid 350 1B 59.0% 0.55 25-702.5 6% Unicid 350 1C 57.2% 0.72 25-80 2.6 2% Unicid 350 1C 54.8% 1.02 ″2.7 6% Unicid 350 1F 55.0% 0.69  30-100 2.8 6% Unicid 350 1G 55.6% 0.71 25-100 2.9 6% Unicid 350 1H 50.6% 0.70  50-110 2.10 6% Unicid 350 1D50.9% 0.84 30-80 2.11 2% Unicid 350 1D 53.0% 0.95 ″ 2.12 3% erucic acid1D 48.4% 0.85 ″ 2.13 3% oleic acid 1D 55.6% 2.23 ″ 2.14 2% Unicid 350 +1D 55.2% 1.17 ″ 2% Stanfax 318 2.15 2% Unicid 350 + 1D 54.1% 1.05 ″ 4%Stanfax 318 2.16 2% Unicid 350 + 1D 58.2% 1.56 ″ 2% oleic acid 2.17 2%Unicid 350 + 1D 51.8% 1.06 ″ 2% Steol CS 130 2.18 4% Unicid 350 1K 50.1%0.75 25-75

In Dispersions 2.14, 2.15 and 2.17, the Stanfax and Steol products areadded to perform as the Frothing Surfactant in a following frothingstep.

EXAMPLE 3 Froth and Foam Preparation

Samples 3A, B, C and D of dispersions are prepared in similar fashion asthose designated above in Table 2 as Dispersion 2.10 and Dispersion 2.12from Polymer 1D. Sample 3A uses 6% Unicid 350 dispersant, while Samples3B, C and D each use 3% erucic acid as dispersant in preparation of thebase dispersion. Each of the dispersion Samples 3A-D is frothed with 1%Steol CS-130 surfactant, together with 0.2% active weight of MethocelE4M hydroxypropyl methylcellulose in the manner described earlier. Thefroths of the ethylene/1-octene copolymers are dried at approximately167 deg F. (75 deg C.), and that of the ethylene/1-butene copolymer atapproximately 140 deg F. (60 deg C.), in a forced air oven. Sample 3D isdried in a slightly different fashion, being placed in an infraredheated “oven” and passed through quickly first, before being placed inthe standard forced air oven to complete the drying process. This servesto more quickly dry the foam surface than the other technique. Whenexamined using SEM, the open cell foams from dispersions 3A through Dexhibit cell size gradient from small cells on the outer surface tolarger cells in the interior of a foam sheet sample. The character ofthe foam cell size for all foams is relatively similar, having about 70%to 80% of the cells of size less than 50 microns, about 10-15% of cellsize between 50 and 100 microns and about 10% greater than 100 micronscell size. Foam density for the 4 foam samples vary from 73 g/L forSample 3A, 97 g/L for Sample 3B, 44 g/L for Sample 3C and 56 g/L forSample 3D.

EXAMPLE 4 Additional Foam Preparations & Testing

In the fashion of Example 3, several different dispersions are prepared,frothed and dried to durable foam. Formulations of the dispersion andfroth blends are shown below in Table 3.

Wicking Height Testing

Vertical wicking testing of foams prepared as described above isconducted for 5 minutes in the fashion described earlier with 0.9%saline solution. The results suggest that highly hydrophobic dispersantssuch as the Unicid dispersants render a resulting foam relativelyhydrophobic and therefore do not wick aqueous fluid well, but are usefulfor absorbing hydrophobic fluids (oil spill clean-up, etc.). Aqueouswicking typically improves when less of a hydrophobic dispersant isused.

TABLE 3 Polymer Foam Characteristics (active component percentages,based on Polymer weight) Dispersion Poly- Dispersant Frothing MethocelWicking Designation mer & amount Surfactant E4M amt. Ht. (cm) 3.1 1AUnicid 425 Stanfax 318 0.4% 0 6% 1.7% 3.2 1B Unicid 350 Steol CS-1300.1% 1.4 6% 2% 3.3 1C Unicid 350 Na Lauryl 0.3% 1.0 2% sulfate 1.5% 3.41E Unicid 425 Steol CS-130 0.2% 0 6% 1% 3.5 1J Unicid 350 Stanfax 318 -none - 0.5 6% 3.3% 3.6 1D Unicid 350 Steol CS-130 0.2% 0 6% 1% 3.7 1DErucic acid Steol CS-130 0.2% 3.0 3% 1% 3.8 1D Erucic acid Stanfax 3180.3% 1.5 3% 1% 3.9 1D Oleic acid - none - 0.2% 2.1 6% (Oleic acid(serves dual purpose) 3.10 1D Oleic acid - none - 0.2% — 3% (Oleic acid3.11 1K Unicid 350 Oleic acid 0.4% 0.2 4% 0.4%

EXAMPLE 5 Filler Additive

A sample of foam is prepared in the manner described for Foam 3.7 inExample 4, above, except that about 14% of a cotton fiber (of about0.15-0.25 in, average fiber length) is added to the blending step beforethe dispersion is frothed and dried to prepare the Foam of theinvention. The resultant Foam is very uniform, has excellent flexibilityand softness and exhibits good absorbency and improved rewettingcapabilities and a less elastic character and higher tensile strength,than the same Foam without the cotton fiber additive.

EXAMPLE 6 Foam Laminate Structure

A sample of Froth is prepared in the manner described for Foam 3.7 inExample 4, above, except that the prepared Froth is doctored onto asheet about 2 mm thick and 75 mm wide of an open-cell (over 80 volumepercent open) extruded polyolefin foam. The Froth is then dried on thatsheet in a forced air oven at 75 deg C. for 30 minutes. The extrudedpolyolefin foam is prepared by extrusion of a thermoplastic melt througha multi-orifice die, using apparatus and techniques described in U.S.Pat. Nos. 3,573,152 and 4,824,720 (each of which is incorporated here byreference). The blend of polyolefin resins in the thermoplastic melt hasa medium flexural modulus (about 110 kpsi by ASTM D790), and to the meltis added suitable amounts of nucleating agent, blowing agent and otheroptional additives if desired. Based on weight of the melt, as anucleating agent about 0.5% talc is employed, and about 3.5% iso-butaneand 4% carbon dioxide are employed as blowing agents, to prepare theextruded polyolefin foam sheet.

The surface of the recovered extruded profile is skived to remove a thinskin or closed cells on the surface and to expose an open-cell surfaceof average cell size about 580 microns (as determined according to ASTMD2856-A). Then a thin foam layer is sliced from that skived surface toyield a foam sheet of desired predetermined thickness of about 2 mm. Thedrying step noted above causes good bonding of the Froth-derived Foam tothe extruded foam's skived surface at the drying temperature to beemployed.

EXAMPLE 7 Post Drying Foam Cell Structure Re-Orientation

In the manner described previously in Example 3, a sample of foam isprepared from a frothed dispersion of AFFINITY EG 8200 resin, anethylene/1-octene, 62%/38% copolymer of melting range approximately30-80 deg C., a density of 0.870 g/cc and 5 g/cc melt index (ASTM D 1238@ 190 deg C./2.16 kg) available from The Dow Chemical Company. Adispersion of same having about 55 wt % (dry) polymer solids and averageparticle size of about 1 micron, prepared using 2% Unicid 350 dispersantand 2% Hystrene 4516 frothing surfactant (a high purity, fatty acidsmixture, typically comprising about 55% stearic, 42% palmitic and 0.5 to1.5% each of margaric, myristic and pentadecanoic acids available fromHumko Chemical Div. of Witco Corp., Memphis, Tenn., and subsequentlyneutralized with potassium hydroxide to form the acid salts) is frothed,doctored on a conveyer belt and thereafter dried to give a foam ofdensity about 0.025 g/cc. Drying is carried out continuously byconveying the froth through a Blue M forced air oven at temperature ofabout 75 deg C. Total time in the drying environment is about 7 to 9minutes, on average. The resulting foam sheet layer is fed, at speeds ofbetween 5 and 25 feet/min (about 150 to 750 cm/min) through the nip oftwo rollers. One roller (rubber coated) is unheated and contacts a MajorSurface of the foam at a temperature of 22 deg C., while the secondroller (steel) is heated to contact the opposite Major Surface atvarying temperatures between about 22 and 55 deg C. (˜72 to 131 deg F.).Pressure applied to the foam sheet layer by the rollers, in asubstantially uniform fashion across each Major Surface, is variedbetween about 10 psig to about 80 psig (about 70 kPa to about 550 kPa,gauge pressure). The original sheet thickness ranges from about 3.42 toabout 3.78 mm. After the sheet is heated, compressed and cooled, samplesare measured for their reduction in thickness between the two MajorSurfaces. Then duplicate strips are cut from each sample and subjectedto the VWH test as previously discussed. The heat and pressureconditions and the properties of the processed foam samples are recordedin Table 4, found below. A “+” sign indicates that VWH exceeds thelength of the sample strips. Foam from Froth made as described, usingthe long chain fatty acid salts (e.g., Hystrene 4516) has a fabric-like“hand”, that is a soft, fabric-like surface is imparted to the finishedFoam, in contrast to Foams made from Froth not containing such fattyacids.

TABLE 4 Foam Treatment Conditions and Resultant VWH CharacteristicsCompression + 48 hrs Samples Roller Roller Original Thickness ThicknessVertical Speed Pressure Roller Foam Compression + % of Orig.Compression + Compression + % of Orig. Wicking Ht. (ft/min)/ (psig/ TempThickness 5 minutes - Thick 24 hours 48 hours - Thick (VWH) Sample *(m/min) kPag) (° C.) (mm) (mm) (%) (mm) (mm) (%) (cm) 1, 2 5/1.5 10/69 22 3.64 3.22 88 3.32 3.30 91 1.6  3, 4 5/1.5 30/207 22 3.78 3.41 90 3.553.57 95 1.65 5, 6 5/1.5 80/552 22 3.61 3.36 93 3.48 3.48 97 1.55 7, 85/1.5 80/552 38 3.49 2.99 85 3.29 3.19 91 2.25  9, 10 5/1.5 80/552 473.42 2.25 66 2.43 2.46 72 9.1+ 11, 12 5/1.5 80/552 50 3.57 2.04 57 2.062.05 57 9.1+ 13, 14 5/1.5 80/552 55 3.61 0.86 24 0.88 0.88 24 10+   15,16 10/3.1  80/552 55 3.51 1.90 54 1.92 1.90 54 8.5  17, 18 18/5.5 80/552 55 3.72 2.42 65 2.49 2.55 68 10+   19, 20 Control No com- — 3.64— — — — — 1.15 pression * Data from average of two samples.

1. A method of making a durable, open-cell foam comprising the steps of:(1) generating a stable, aqueous froth comprising a) one or morecopolymers or interpolymers of ethylene and/or 1-propene with or withoutother monomers selected from C₄ to C₁₀ olefins and having an ethylene or1-propene content from about 2-98 weight percent; b) water; c) afrothing surfactant; and d) a gas; where the components comprise about:a) 35 to 75 percent, b) 35 to 75 percent and c) 1 to 6 percent of thecombined weight of a), b) and c), and d) is present in an amount suchthat d) comprises at least 80 percent of the total volume of allcomponents present in the froth; (2) thereafter subjecting said froth toat least one drying energy source to provide a durable, open-cell foam,in a fashion such that the volume of said resulting foam consists of notless than 70 volume percent of the volume of said froth; and (3)thereafter recovering the durable, open-cell foam.
 2. The method ofclaim 1 wherein the froth of component (1) further comprises componente) a foam stabilizer selected from: alkylcellulose ethers, hydroxyalkylcellulose ethers, hydroxyalkyl alkylcellulose ethers, guar gum, xanthangum, and polyoxyethylene resins of at least 20,000 molecular weight,said component e) present in the amount of from about 0.05 to about 2percent based on the dry weight of component a) polymer.
 3. The methodof claim 1 where, in the froth of component (1), component a) is acopolymer of ethylene with an alpha-olefin comonomer of from 3 to 10carbon atoms.
 4. The method of claim 3 where the alpha-olefin comonomerof component a) is selected from 1-propene, 1-butene, 1-hexene and1-octene and component a) has a melt index between about 0.5 and about30 g/10 min as determined by ASTM D1238 (condition 190 deg C./2.16 kg).5. The method of claim 1 wherein step (2) the drying energy source isselected from a heated air generator, an infrared ray generator, adielectric heating device, and any combination or multiplicity thereof.6. The method of claim 1 further characterized in that the froth iscontinuously generated and thereafter said froth is continuouslysubjected to the at least one drying energy source.
 7. The method ofclaim 1 further characterized in that said froth in step (2) issubjected to a combination of at least two drying energy sources, eithersimultaneously or in sequence.
 8. The method of claim 7 where in step(2) the drying energy sources are selected from at least one heated airgenerator, at least one infrared ray generator and at least onedielectric heating device.
 9. The method of claim 1 furthercharacterized in that prior to or after recovery the open cell foam is,on at least one major surface, subjected to heating that softenssubstantially all of such major surface to a distance of at least 2percent of the foam's initial thickness below the surface, and while sosoftened a major portion of that major surface is compressed with apressure sufficient to convert a plurality of cells, at or near thatmajor surface, to a three-dimensional ellipsoidal shape the major axisof which is aligned generally parallel to said major surface.